diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5ccde69..09710bd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,12 @@ et [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Ajouté
 
+- **#89 Drag & Drop complet de fichiers/dossiers & intégration Assistant IA** — solution
+  complète de glisser-déposer de fichiers individuels, multiples et **dossiers récursifs**
+  depuis l'OS vers le vault (`POST /api/vault/{vault}/batch-upload`, FileSystem API),
+  overlay plein écran à double cible (dépôt vault vs analyse IA), surbrillance des cibles dans
+  l'arborescence, et dropzone BooksLM pour injection de contexte ou pièces jointes.
+  Fiche : [docs/features/drag-and-drop-ai.md](./docs/features/drag-and-drop-ai.md).
 - **#88 Assistant IA : contexte applicatif** — l'assistant en mode **Général**
   reçoit l'état vivant de l'interface (`app_context`) et connaît désormais les
   documents ouverts, le répertoire et le vault courants, la recherche en cours
diff --git a/backend/main.py b/backend/main.py
index bf6570a..89e9a32 100644
--- a/backend/main.py
+++ b/backend/main.py
@@ -105,6 +105,9 @@ from backend.services.backups import list_backup_files as service_list_backup_fi
 from backend.services.errors import ServiceError
 from backend.services.files import read_raw_file
 from backend.services.graph import get_graph as service_get_graph
+from backend.services.mutations import (
+    batch_upload_files as service_batch_upload_files,
+)
 from backend.services.mutations import (
     create_directory as service_create_directory,
 )
@@ -436,6 +439,31 @@ class FileCreateResponse(BaseModel):
     path: str = Field(description="Path of the created file")
 
 
+class BatchUploadFileItem(BaseModel):
+    """A single file/dir entry in a batch upload request."""
+    path: str = Field(description="Relative path of the item within the batch")
+    content: str | None = Field(default=None, description="Base64 encoded or text content for files")
+    is_dir: bool = Field(default=False, description="True if entry represents an empty directory")
+
+
+class BatchUploadRequest(BaseModel):
+    """Request payload for batch file/directory upload."""
+    target_dir: str = Field(default="", description="Base directory in vault to upload into (empty for root)")
+    files: list[BatchUploadFileItem] = Field(description="List of files and directories to upload")
+    overwrite: bool = Field(default=True, description="Whether to overwrite existing files (creates backups)")
+
+
+class BatchUploadResponse(BaseModel):
+    """Response from batch file/directory upload."""
+    success: bool = Field(description="True if all files uploaded without error")
+    vault: str = Field(description="Vault name")
+    target_dir: str = Field(description="Target directory")
+    uploaded: list[str] = Field(description="List of created/updated file paths")
+    created_dirs: list[str] = Field(description="List of created directory paths")
+    errors: list[dict[str, Any]] = Field(default_factory=list, description="List of items that failed")
+    total_files: int = Field(description="Total uploaded files count")
+
+
 class FileRenameRequest(BaseModel):
     """Request to rename a file."""
     path: str = Field(description="Current path of the file")
@@ -1905,6 +1933,78 @@ async def api_file_create(
     return {"success": True, "path": result["path"]}
 
 
+@app.post("/api/vault/{vault_name}/batch-upload", response_model=BatchUploadResponse)
+async def api_batch_upload(
+    vault_name: str,
+    body: BatchUploadRequest,
+    current_user=Depends(require_auth),
+):
+    """Upload multiple files and directories (recursively) into a vault.
+
+    Accepts base64 encoded or plain text files with relative directory paths.
+    Creates missing parent folders safely.
+
+    Args:
+        vault_name: Target vault name.
+        body: BatchUploadRequest with target_dir and files list.
+
+    Returns:
+        BatchUploadResponse with summary of uploaded files and errors.
+    """
+    if not check_vault_access(vault_name, current_user):
+        raise HTTPException(status_code=403, detail=f"Accès refusé à la vault '{vault_name}'")
+
+    import base64
+
+    items: list[dict[str, Any]] = []
+    for f in body.files:
+        if f.is_dir:
+            items.append({"path": f.path, "is_dir": True})
+            continue
+
+        raw_bytes = b""
+        if f.content is not None:
+            # Check if content is base64 encoded data URI or raw base64
+            content_str = f.content
+            if content_str.startswith("data:") and ";base64," in content_str:
+                content_str = content_str.split(";base64,", 1)[1]
+            try:
+                raw_bytes = base64.b64decode(content_str)
+            except Exception:
+                # Fallback to utf-8 text encoding
+                raw_bytes = f.content.encode("utf-8")
+
+        items.append({"path": f.path, "content": raw_bytes, "is_dir": False})
+
+    result = service_batch_upload_files(
+        vault_name,
+        body.target_dir,
+        items,
+        overwrite=body.overwrite,
+    )
+
+    # Update index and SSE notifications for uploaded files
+    for path in result["uploaded"]:
+        try:
+            await update_single_file(vault_name, path)
+            await sse_manager.broadcast("file_created", {
+                "vault": vault_name,
+                "path": path,
+            })
+            await dispatch_webhooks("file_created", {"vault": vault_name, "path": path})
+        except Exception as e:
+            logger.warning(f"Failed to post-process upload of {path}: {e}")
+
+    # SSE notification for tree refresh
+    if result["uploaded"] or result["created_dirs"]:
+        await sse_manager.broadcast("tree_updated", {
+            "vault": vault_name,
+            "target_dir": result["target_dir"],
+        })
+
+    return result
+
+
 @app.patch("/api/file/{vault_name}", response_model=FileRenameResponse)
 async def api_file_rename(
     vault_name: str,
diff --git a/backend/services/mutations.py b/backend/services/mutations.py
index e747dd2..accf6f0 100644
--- a/backend/services/mutations.py
+++ b/backend/services/mutations.py
@@ -44,12 +44,17 @@ def _ensure_writable(root: Path) -> None:
         raise ServiceError("Vault is read-only", code="read_only", status=403)
 
 
-def _validate_extension(file_path: Path) -> None:
+def _validate_extension(file_path: Path, *, allow_images: bool = False) -> None:
     """Reject unsupported file extensions (400)."""
     from backend.indexer import SUPPORTED_EXTENSIONS
 
     ext = file_path.suffix.lower()
-    if ext not in SUPPORTED_EXTENSIONS and file_path.name.lower() not in ("dockerfile", "makefile"):
+    allowed = SUPPORTED_EXTENSIONS
+    if allow_images:
+        from backend.attachment_indexer import IMAGE_EXTENSIONS
+        allowed = allowed | IMAGE_EXTENSIONS
+
+    if ext not in allowed and file_path.name.lower() not in ("dockerfile", "makefile"):
         raise ServiceError(
             f"Unsupported file extension: {ext}",
             code="unsupported_extension",
@@ -684,3 +689,123 @@ def restore_backup(
         "restored_from": version,
         "current_backed_up": current_backed_up,
     }
+
+
+# ── D3. Batch upload & raw file save ───────────────────────────────────────
+
+
+def save_raw_file(
+    vault_name: str,
+    path: str,
+    content: bytes,
+    *,
+    overwrite: bool = True,
+) -> dict[str, Any]:
+    """Save a binary or text file to a vault (e.g. from upload / drag-and-drop).
+
+    Creates parent directories automatically and safely validates the path.
+    Supports supported text extensions, images and Excalidraw files.
+
+    Args:
+        vault_name: Name of the vault.
+        path: Vault-relative path.
+        content: Raw bytes to write.
+        overwrite: When True, replace existing files (with backup).
+
+    Returns:
+        Dict with ``success``, ``vault``, ``path``, and ``size``.
+    """
+    root = get_vault_root(vault_name)
+    _ensure_writable(root)
+    file_path = resolve_safe_path(root, path)
+    _validate_extension(file_path, allow_images=True)
+
+    rel_path = _rel(root, file_path)
+
+    if file_path.exists():
+        if not overwrite:
+            raise ServiceError(
+                f"File already exists: {rel_path}",
+                code="already_exists",
+                status=409,
+                details={"vault": vault_name, "path": rel_path},
+            )
+        create_backup(file_path, vault_name, rel_path)
+
+    try:
+        file_path.parent.mkdir(parents=True, exist_ok=True)
+        file_path.write_bytes(content)
+    except PermissionError as e:
+        raise ServiceError("Permission denied: cannot save file", code="permission_denied", status=403) from e
+
+    logger.info(f"Raw file saved: {vault_name}/{rel_path} ({len(content)} bytes)")
+    return {"success": True, "vault": vault_name, "path": rel_path, "size": len(content)}
+
+
+def batch_upload_files(
+    vault_name: str,
+    target_dir: str,
+    files: list[dict[str, Any]],
+    *,
+    overwrite: bool = True,
+) -> dict[str, Any]:
+    """Process a batch of uploaded files and directories into a vault.
+
+    Args:
+        vault_name: Name of the target vault.
+        target_dir: Base directory inside the vault (empty string for root).
+        files: List of dicts, each with:
+            - ``path``: relative path within the batch (e.g. ``"sub/doc.md"`` or ``"note.md"``).
+            - ``content``: bytes content (or base64 decoded).
+            - ``is_dir``: optional boolean for empty directories.
+        overwrite: Whether to overwrite existing files.
+
+    Returns:
+        Dict with ``uploaded`` (list of paths), ``created_dirs`` (list of paths),
+        and ``errors`` (list of error dicts).
+    """
+    root = get_vault_root(vault_name)
+    _ensure_writable(root)
+
+    clean_target = (target_dir or "").strip().strip("/\\")
+    uploaded: list[str] = []
+    created_dirs: list[str] = []
+    errors: list[dict[str, Any]] = []
+
+    for item in files:
+        rel_subpath = (item.get("path") or "").strip().replace("\\", "/").lstrip("/")
+        if not rel_subpath:
+            continue
+
+        full_rel_path = f"{clean_target}/{rel_subpath}" if clean_target else rel_subpath
+        is_dir = item.get("is_dir", False)
+
+        if is_dir:
+            try:
+                dir_path = resolve_safe_path(root, full_rel_path)
+                dir_path.mkdir(parents=True, exist_ok=True)
+                created_dirs.append(_rel(root, dir_path))
+            except Exception as e:
+                errors.append({"path": full_rel_path, "error": str(e)})
+            continue
+
+        raw_bytes = item.get("content", b"")
+        if isinstance(raw_bytes, str):
+            raw_bytes = raw_bytes.encode("utf-8")
+
+        try:
+            res = save_raw_file(vault_name, full_rel_path, raw_bytes, overwrite=overwrite)
+            uploaded.append(res["path"])
+        except Exception as e:
+            errors.append({"path": full_rel_path, "error": str(e)})
+
+    return {
+        "success": len(errors) == 0,
+        "vault": vault_name,
+        "target_dir": clean_target,
+        "uploaded": uploaded,
+        "created_dirs": created_dirs,
+        "errors": errors,
+        "total_files": len(uploaded),
+    }
+
diff --git a/docs/ROADMAP.md b/docs/ROADMAP.md
index 625cb12..010259a 100644
--- a/docs/ROADMAP.md
+++ b/docs/ROADMAP.md
@@ -135,6 +135,7 @@
 
 | # | Domaine / fonctionnalité | Version | Détails |
 |---|---|---|---|
+| 89 | Drag & drop complet de fichiers/dossiers & intégration Assistant IA | 2.3.0 | [features/drag-and-drop-ai.md](./features/drag-and-drop-ai.md) |
 | 1–8 | Fondations (FastAPI, TF-IDF + stemming, watchdog, SPA, sécurité, path traversal, gzip, PWA) | 1.0.0→1.4.0 | [archive](./archive/COMPLETED_v1-v2.md) |
 | 9–20 | UX & productivité (share, webhooks, dashboard, conflits, backlinks, redaction, backups, graphe, header, aperçu) | 1.5.0→1.6.0 | [archive](./archive/COMPLETED_v1-v2.md) |
 | 21–22 | Architecture (split `app.js` → 16 modules, validateur imports CI) | 1.5.1 | [archive](./archive/COMPLETED_v1-v2.md) |
diff --git a/docs/features/drag-and-drop-ai.md b/docs/features/drag-and-drop-ai.md
new file mode 100644
index 0000000..0907dc4
--- /dev/null
+++ b/docs/features/drag-and-drop-ai.md
@@ -0,0 +1,71 @@
+# #89 — Drag & drop complet de fichiers / dossiers & intégration Assistant IA
+
+> **Statut :** ✅ Livré  
+> **Priorité :** 🟡 P2  
+> **Zone :** frontend + backend  
+> **Références :** [Roadmap](../ROADMAP.md) · [Assistant IA #80](./ai-assistant-ux.md) · [Assistant IA #88](./ai-app-context.md)
+
+---
+
+## 🎯 Objectif
+
+Offrir une expérience complète de glisser-déposer (Drag & Drop) dans ObsiGate couvrant à la fois la gestion de fichiers dans le vault et les interactions avec l'Assistant IA :
+1. Glisser-déposer de fichiers individuels, multiples et **dossiers récursifs** depuis le système d'exploitation vers l'arborescence du vault.
+2. Espace de drop dédié (dropzone explicite + overlay visuel réactif à double cible).
+3. Glisser-déposer de fichiers / dossiers (internes au vault ou externes depuis l'OS) vers le panneau de l'assistant IA pour enrichir le contexte ou lui soumettre des instructions directes.
+
+---
+
+## 🏗️ Architecture & Composants
+
+### 1. Backend — Endpoint d'upload récursif / batch (`POST /api/vault/{vault}/batch-upload`)
+- Réception de structures de fichiers avec leurs chemins relatifs (`relative_path`).
+- Validation de sécurité anti path-traversal via `resolve_safe_path` et validation d'extension via `_validate_extension(allow_images=True)`.
+- Création automatique et récursive des dossiers parents manquants.
+- Gestion des collisions / écrasements (option d'écrasement avec sauvegarde automatique `create_backup`).
+- Retour d'un bilan d'upload (`uploaded`, `created_dirs`, `errors`).
+
+### 2. Frontend — Core Drag & Drop & Traversée d'arborescence (`frontend/js/upload.js` & `dragdrop.js`)
+- Utilisation de la `FileSystem API` (`DataTransferItem.webkitGetAsEntry()`) pour extraire de manière récursive toute l'arborescence de répertoires et fichiers déposés depuis l'OS.
+- Surbrillance dynamique des dossiers cibles dans l'arborescence (`.tree-item`) lors du survol d'éléments externes de type `Files`.
+- Support du drop sur la racine d'un vault ou dans un sous-dossier spécifique.
+- Feedback utilisateur immédiat via les toasts d'information / progression / succès.
+
+### 3. Frontend — Dropzones dédiées & Overlay global
+- Overlay visuel plein écran lors du drag d'éléments depuis l'OS sur l'application avec séparation claire des zones cibles :
+  - *Zone Vault* : Déposer pour importer dans le dossier actif / vault.
+  - *Zone Assistant IA* : Déposer pour analyser avec l'IA.
+- Dropzone réactive dans le panneau BooksLM.
+
+### 4. Intégration Assistant IA (`frontend/js/bookslm.js`)
+- **Drag interne (depuis l'arborescence ObsiGate vers le chat)** :
+  - Déposer un dossier : bascule l'assistant ou insère le dossier en contexte ad-hoc.
+  - Déposer un ou plusieurs fichiers : ajoute les fichiers en context chips (`_adhocFiles`).
+- **Drag externe (depuis l'OS vers le chat)** :
+  - Images : ajout direct en pièce jointe pour les modèles multimodaux (vision).
+  - Documents texte / Markdown / Code : lecture immédiate du contenu et ajout en contexte ad-hoc.
+
+---
+
+## 📋 Sous-tâches
+
+- [x] **Backend** :
+  - [x] Endpoint `POST /api/vault/{vault}/batch-upload` (gestion des sous-dossiers et upload en batch).
+  - [x] Services métier `save_raw_file` et `batch_upload_files` dans `backend/services/mutations.py`.
+  - [x] Tests unitaires backend (`tests/test_batch_upload.py`).
+- [x] **Frontend Core Upload & Tree Drop** :
+  - [x] Helper de lecture récursive `readDataTransferEntries` (fichiers + dossiers) dans `frontend/js/upload.js`.
+  - [x] Écouteurs `dragover` / `drop` sur l'arborescence du vault avec retour visuel dans `frontend/js/dragdrop.js`.
+  - [x] Gestion des transferts et notifications toasts.
+- [x] **Overlay & Dropzone UI** :
+  - [x] Détection globale du glisser externe sur la fenêtre avec overlay interactif (`initGlobalDropOverlay`).
+  - [x] Styles de l'overlay et des zones cibles dans `frontend/style.css`.
+- [x] **Intégration Assistant IA** :
+  - [x] Dropzone sur le composeur BooksLM (`_setupDropZones`).
+  - [x] Gestion des drops internes (fichiers/dossiers du vault) et externes (OS `handleExternalDroppedItems`).
+  - [x] Intégration transparente avec les chips de contexte et images multimodales.
+- [x] **Internationalisation (i18n)** :
+  - [x] Clés FR/EN pour toutes les indications de drop, progression et erreurs dans `frontend/locales/{fr,en}.json`.
+- [x] **Tests & Validation** :
+  - [x] Tests unitaires frontend `tests/frontend/upload.test.mjs`.
+  - [x] Validation de tous les imports/exports ES modules `tests/frontend/validate-imports.mjs`.
diff --git a/frontend/js/bookslm.js b/frontend/js/bookslm.js
index 1368cd2..8818e84 100644
--- a/frontend/js/bookslm.js
+++ b/frontend/js/bookslm.js
@@ -965,6 +965,12 @@ class BooksLM {
       this._sendMessage();
     });
 
+    // Setup Drag & Drop for internal items and external files (#89)
+    this._setupDropZones(panel);
+
+    // Save singleton reference on window
+    window.BooksLMInstance = this;
+
     return panel;
   }
 
@@ -981,6 +987,93 @@ class BooksLM {
     return Math.max(PANEL_MIN_WIDTH, Math.min(PANEL_MAX_WIDTH, width));
   }
 
+  _setupDropZones(panel) {
+    const composer = panel.querySelector('.bookslm-composer') || panel;
+
+    const onDragOver = (e) => {
+      e.preventDefault();
+      e.stopPropagation();
+      e.dataTransfer.dropEffect = 'copy';
+      composer.classList.add('bookslm-drop-over');
+    };
+
+    const onDragLeave = (e) => {
+      if (composer.contains(e.relatedTarget)) return;
+      composer.classList.remove('bookslm-drop-over');
+    };
+
+    const onDrop = async (e) => {
+      e.preventDefault();
+      e.stopPropagation();
+      composer.classList.remove('bookslm-drop-over');
+
+      // Check if internal tree drag
+      const treeData = e.dataTransfer.getData('tree:path') || e.dataTransfer.getData('text/plain');
+      const treeVault = e.dataTransfer.getData('tree:vault');
+      const treeType = e.dataTransfer.getData('tree:type');
+
+      if (treeData && treeVault) {
+        if (treeType === 'directory') {
+          this._addAdhocDir(treeData, treeVault);
+        } else {
+          this._addAdhocFile(treeData, treeVault);
+        }
+        return;
+      }
+
+      // External files
+      const files = Array.from(e.dataTransfer.files || []);
+      if (files.length > 0) {
+        this.handleExternalDroppedItems(files.map((f) => ({ path: f.name, file: f, isDir: false })));
+      }
+    };
+
+    composer.addEventListener('dragover', onDragOver);
+    composer.addEventListener('dragleave', onDragLeave);
+    composer.addEventListener('drop', onDrop);
+  }
+
+  /**
+   * Handle files/folders dropped from outside into BooksLM (#89).
+   */
+  async handleExternalDroppedItems(items) {
+    if (!this._isOpen) {
+      this.open();
+    }
+
+    for (const item of items) {
+      if (item.isDir) {
+        continue;
+      }
+      const file = item.file;
+      if (!file) continue;
+
+      if (file.type && file.type.startsWith('image/')) {
+        this._addImageFile(file);
+      } else {
+        // Read text/markdown file content
+        try {
+          const text = await new Promise((resolve, reject) => {
+            const reader = new FileReader();
+            reader.onload = () => resolve(String(reader.result || ''));
+            reader.onerror = reject;
+            reader.readAsText(file);
+          });
+
+          // Insert into context files or append to composer
+          this._adhocFiles.push({
+            path: item.path,
+            vault: null,
+            inlineContent: text,
+          });
+          this._renderAttachments();
+        } catch (err) {
+          console.warn('Could not read dropped file as text:', err);
+        }
+      }
+    }
+  }
+
   _startResize(e) {
     if (!this._panel || this._isFullscreen) return;
     e.preventDefault();
diff --git a/frontend/js/dragdrop.js b/frontend/js/dragdrop.js
index e5cbb1c..4ccca93 100644
--- a/frontend/js/dragdrop.js
+++ b/frontend/js/dragdrop.js
@@ -9,8 +9,10 @@
  */
 
 import { api } from './auth.js';
+import { t } from './i18n.js';
 import { showToast } from './ui.js';
 import { refreshSidebarTreePreservingState } from './sidebar.js';
+import { readDataTransferEntries, handleVaultDropUpload } from './upload.js';
 
 // ---------------------------------------------------------------------------
 // State
@@ -180,14 +182,21 @@ function onDragStart(e) {
 }
 
 function onDragOver(e) {
-  if (!dragState) return;
+  const isExternalFiles = e.dataTransfer && Array.from(e.dataTransfer.types || []).includes('Files');
+
+  if (!dragState && !isExternalFiles) return;
   e.preventDefault(); // Required to allow drop
-  e.dataTransfer.dropEffect = 'move';
+
+  if (isExternalFiles) {
+    e.dataTransfer.dropEffect = 'copy';
+  } else {
+    e.dataTransfer.dropEffect = 'move';
+  }
 
   clearAllHighlights();
 
   const target = getDropTarget(e.target);
-  if (!target || isInvalidDrop(dragState, target)) {
+  if (!target || (!isExternalFiles && isInvalidDrop(dragState, target))) {
     e.dataTransfer.dropEffect = 'none';
     return;
   }
@@ -224,17 +233,33 @@ async function onDrop(e) {
   e.preventDefault();
   e.stopPropagation();
 
-  if (!dragState) return;
+  const isExternalFiles = e.dataTransfer && (
+    (e.dataTransfer.files && e.dataTransfer.files.length > 0) ||
+    (e.dataTransfer.items && e.dataTransfer.items.length > 0) ||
+    Array.from(e.dataTransfer.types || []).includes('Files')
+  );
+
+  if (!dragState && !isExternalFiles) return;
 
   const target = getDropTarget(e.target);
-  if (!target || isInvalidDrop(dragState, target)) {
+  if (!target || (!isExternalFiles && isInvalidDrop(dragState, target))) {
     onDragEnd();
     return;
   }
 
-  const { vault, path, type } = dragState;
   const { vault: targetVault, targetDir } = target;
 
+  if (isExternalFiles) {
+    onDragEnd();
+    const items = await readDataTransferEntries(e.dataTransfer.items || e.dataTransfer.files);
+    if (items.length > 0) {
+      await handleVaultDropUpload(targetVault, targetDir, items);
+    }
+    return;
+  }
+
+  const { vault, path, type } = dragState;
+
   // Don't move if source and target are the same vault
   if (vault !== targetVault) {
     showToast(t('dragdrop.cross_vault_unsupported'), 'error');
@@ -312,6 +337,119 @@ export function initDragDrop() {
     makeAllDraggable();
   });
   observer.observe(container, { childList: true, subtree: true });
+
+  // Initialize global drop overlay
+  initGlobalDropOverlay();
+}
+
+/**
+ * Initialize a global dropzone overlay across the entire window
+ * when dragging files/folders from the OS.
+ */
+export function initGlobalDropOverlay() {
+  if (document.getElementById('obsigate-global-drop-overlay')) return;
+
+  const overlay = document.createElement('div');
+  overlay.id = 'obsigate-global-drop-overlay';
+  overlay.className = 'obsigate-drop-overlay';
+  overlay.innerHTML = `
+    <div class="obsigate-drop-backdrop"></div>
+    <div class="obsigate-drop-modal">
+      <h2 class="obsigate-drop-title">${t('dragdrop.overlay_title') || 'Déposer des fichiers ou dossiers'}</h2>
+      <div class="obsigate-drop-zones">
+        <div class="obsigate-drop-zone obsigate-drop-vault" data-zone="vault">
+          <div class="obsigate-drop-zone-icon">📁</div>
+          <div class="obsigate-drop-zone-title">${t('dragdrop.overlay_vault_zone') || 'Importer dans le Vault'}</div>
+          <div class="obsigate-drop-zone-desc" id="obsigate-drop-vault-target"></div>
+        </div>
+        <div class="obsigate-drop-zone obsigate-drop-ai" data-zone="ai">
+          <div class="obsigate-drop-zone-icon">🧠</div>
+          <div class="obsigate-drop-zone-title">${t('dragdrop.overlay_ai_zone') || "Analyser avec l'Assistant IA"}</div>
+          <div class="obsigate-drop-zone-desc">Envoyer au chat BooksLM</div>
+        </div>
+      </div>
+    </div>
+  `;
+  document.body.appendChild(overlay);
+
+  let dragCounter = 0;
+
+  window.addEventListener('dragenter', (e) => {
+    if (dragState) return; // Don't show global overlay for internal tree reordering
+    const types = Array.from(e.dataTransfer?.types || []);
+    if (!types.includes('Files')) return;
+
+    dragCounter++;
+    if (dragCounter === 1) {
+      // Update target vault description
+      const activeVault = window.state?.activeVault || (document.querySelector('.tree-item.vault-item')?.dataset?.vault) || '';
+      const vaultDesc = overlay.querySelector('#obsigate-drop-vault-target');
+      if (vaultDesc) {
+        vaultDesc.textContent = activeVault ? `Vault : ${activeVault}` : 'Vault par défaut';
+      }
+      overlay.classList.add('active');
+    }
+  });
+
+  window.addEventListener('dragleave', (e) => {
+    if (dragState) return;
+    const types = Array.from(e.dataTransfer?.types || []);
+    if (!types.includes('Files')) return;
+
+    dragCounter--;
+    if (dragCounter <= 0) {
+      dragCounter = 0;
+      overlay.classList.remove('active');
+    }
+  });
+
+  window.addEventListener('dragover', (e) => {
+    const types = Array.from(e.dataTransfer?.types || []);
+    if (!types.includes('Files')) return;
+    e.preventDefault();
+  });
+
+  const zones = overlay.querySelectorAll('.obsigate-drop-zone');
+  zones.forEach((zone) => {
+    zone.addEventListener('dragover', (e) => {
+      e.preventDefault();
+      e.stopPropagation();
+      e.dataTransfer.dropEffect = 'copy';
+      zone.classList.add('hover');
+    });
+
+    zone.addEventListener('dragleave', () => {
+      zone.classList.remove('hover');
+    });
+
+    zone.addEventListener('drop', async (e) => {
+      e.preventDefault();
+      e.stopPropagation();
+      dragCounter = 0;
+      overlay.classList.remove('active');
+      zone.classList.remove('hover');
+
+      const zoneType = zone.dataset.zone;
+      const items = await readDataTransferEntries(e.dataTransfer.items || e.dataTransfer.files);
+      if (!items.length) return;
+
+      if (zoneType === 'vault') {
+        const activeVault = window.state?.activeVault || (document.querySelector('.tree-item.vault-item')?.dataset?.vault);
+        if (activeVault) {
+          await handleVaultDropUpload(activeVault, '', items);
+        } else {
+          showToast('Aucun vault sélectionné', 'error');
+        }
+      } else if (zoneType === 'ai') {
+        // Dispatch or pass to BooksLM assistant
+        if (window.BooksLMInstance) {
+          window.BooksLMInstance.handleExternalDroppedItems(items);
+        } else {
+          showToast("Assistant IA non initialisé", 'warning');
+        }
+      }
+    });
+  });
 }
 
 /**
diff --git a/frontend/js/upload.js b/frontend/js/upload.js
new file mode 100644
index 0000000..737ab94
--- /dev/null
+++ b/frontend/js/upload.js
@@ -0,0 +1,205 @@
+/**
+ * ObsiGate — File & Folder Upload & Drag-and-Drop Core Module (#89).
+ *
+ * Provides utilities for:
+ * - Traversing recursive directories and files from DataTransfer / FileSystem API
+ * - Reading files into base64 / text payloads
+ * - Batch uploading to `/api/vault/{vault}/batch-upload`
+ * - Managing drop progress modals and confirmation dialogs
+ */
+
+import { api } from './auth.js';
+import { t } from './i18n.js';
+import { showToast } from './ui.js';
+import { refreshSidebarTreePreservingState } from './sidebar.js';
+
+/**
+ * Recursively read all FileSystemEntry items (files and directories) from DataTransferItemList.
+ * Falls back to plain File objects if FileSystem API is unavailable.
+ *
+ * @param {DataTransferItemList|FileList|File[]} items - DataTransfer items or files
+ * @returns {Promise<Array<{ path: string, file?: File, isDir?: boolean }>>}
+ */
+export async function readDataTransferEntries(items) {
+  const results = [];
+  if (!items) return results;
+
+  // Check if items support webkitGetAsEntry
+  const entries = [];
+  if (items.length && typeof items[0].webkitGetAsEntry === 'function') {
+    for (let i = 0; i < items.length; i++) {
+      const entry = items[i].webkitGetAsEntry();
+      if (entry) entries.push(entry);
+    }
+  }
+
+  if (entries.length > 0) {
+    // Traverse entries recursively
+    for (const entry of entries) {
+      await traverseFileSystemEntry(entry, '', results);
+    }
+  } else {
+    // Plain FileList or files
+    for (let i = 0; i < items.length; i++) {
+      const file = items[i] instanceof File ? items[i] : items[i].getAsFile ? items[i].getAsFile() : null;
+      if (file) {
+        const relPath = file.webkitRelativePath || file.name;
+        results.push({
+          path: relPath.replace(/\\/g, '/'),
+          file,
+          isDir: false,
+        });
+      }
+    }
+  }
+
+  return results;
+}
+
+/**
+ * Traverse a single FileSystemEntry recursively.
+ */
+async function traverseFileSystemEntry(entry, parentPath, results) {
+  const currentPath = parentPath ? `${parentPath}/${entry.name}` : entry.name;
+
+  if (entry.isFile) {
+    const file = await new Promise((resolve, reject) => {
+      entry.file(resolve, reject);
+    });
+    results.push({
+      path: currentPath.replace(/\\/g, '/'),
+      file,
+      isDir: false,
+    });
+  } else if (entry.isDirectory) {
+    results.push({
+      path: currentPath.replace(/\\/g, '/'),
+      isDir: true,
+    });
+    const dirReader = entry.createReader();
+    const readAllEntries = async () => {
+      const childEntries = await new Promise((resolve, reject) => {
+        dirReader.readEntries(resolve, reject);
+      });
+      if (childEntries.length > 0) {
+        for (const child of childEntries) {
+          await traverseFileSystemEntry(child, currentPath, results);
+        }
+        await readAllEntries(); // Read next batch (readEntries returns max 100 at a time)
+      }
+    };
+    await readAllEntries();
+  }
+}
+
+/**
+ * Convert a File object to base64 data string.
+ * @param {File} file
+ * @returns {Promise<string>}
+ */
+export function fileToBase64(file) {
+  return new Promise((resolve, reject) => {
+    const reader = new FileReader();
+    reader.onload = () => {
+      const res = reader.result;
+      if (typeof res === 'string') {
+        resolve(res);
+      } else {
+        reject(new Error('Failed to read file as base64 string'));
+      }
+    };
+    reader.onerror = (err) => reject(err);
+    reader.readAsDataURL(file);
+  });
+}
+
+/**
+ * Upload a batch of extracted items into a vault and target folder.
+ *
+ * @param {string} vault - Target vault name
+ * @param {string} targetDir - Target relative directory (empty for root)
+ * @param {Array<{ path: string, file?: File, isDir?: boolean }>} items - Extracted items
+ * @param {Object} [options]
+ * @param {boolean} [options.overwrite=true]
+ * @param {Function} [options.onProgress] - Callback (current, total)
+ * @returns {Promise<{ success: boolean, uploaded: string[], created_dirs: string[], errors: any[] }>}
+ */
+export async function uploadBatch(vault, targetDir, items, options = {}) {
+  if (!vault || !items || !items.length) {
+    return { success: true, uploaded: [], created_dirs: [], errors: [], total_files: 0 };
+  }
+
+  const { overwrite = true, onProgress = null } = options;
+  const payloadFiles = [];
+  const total = items.length;
+
+  for (let i = 0; i < total; i++) {
+    const item = items[i];
+    if (onProgress) onProgress(i, total, item.path);
+
+    if (item.isDir) {
+      payloadFiles.push({
+        path: item.path,
+        is_dir: true,
+      });
+    } else if (item.file) {
+      try {
+        const b64 = await fileToBase64(item.file);
+        payloadFiles.push({
+          path: item.path,
+          content: b64,
+          is_dir: false,
+        });
+      } catch (err) {
+        console.warn(`Failed to encode file ${item.path}:`, err);
+      }
+    }
+  }
+
+  if (onProgress) onProgress(total, total, 'Sending payload...');
+
+  const response = await api(`/api/vault/${encodeURIComponent(vault)}/batch-upload`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({
+      target_dir: targetDir || '',
+      files: payloadFiles,
+      overwrite,
+    }),
+  });
+
+  return response;
+}
+
+/**
+ * Show a simple upload modal / toast and execute the upload.
+ *
+ * @param {string} vault
+ * @param {string} targetDir
+ * @param {Array<{ path: string, file?: File, isDir?: boolean }>} items
+ */
+export async function handleVaultDropUpload(vault, targetDir, items) {
+  if (!items || !items.length) return;
+
+  const fileCount = items.filter((x) => !x.isDir).length;
+  const dirCount = items.filter((x) => x.isDir).length;
+  const destName = targetDir ? `${vault}/${targetDir}` : vault;
+
+  showToast(`${t('upload.uploading', { count: fileCount }) || `Uploading ${fileCount} file(s) to ${destName}...`}`, 'info');
+
+  try {
+    const res = await uploadBatch(vault, targetDir, items);
+    if (res && res.success) {
+      showToast(t('upload.success', { count: res.uploaded.length }) || `Imported ${res.uploaded.length} file(s) successfully`, 'success');
+    } else if (res && res.uploaded && res.uploaded.length > 0) {
+      showToast(t('upload.partial', { count: res.uploaded.length, errors: res.errors.length }) || `Imported ${res.uploaded.length} file(s) (${res.errors.length} errors)`, 'warning');
+    } else {
+      const errDetail = res?.errors?.[0]?.error || 'Unknown error';
+      showToast(`${t('upload.error') || 'Upload failed'}: ${errDetail}`, 'error');
+    }
+    await refreshSidebarTreePreservingState();
+  } catch (err) {
+    console.error('Batch upload error:', err);
+    showToast(`${t('upload.error') || 'Upload failed'}: ${err.message || err}`, 'error');
+  }
+}
diff --git a/frontend/locales/en.json b/frontend/locales/en.json
index 6ed6075..fd5177e 100644
--- a/frontend/locales/en.json
+++ b/frontend/locales/en.json
@@ -634,6 +634,13 @@
   "dashboard.zero_files": "0 files",
   "dragdrop.cross_vault_unsupported": "Cross-vault moves are not supported",
   "dragdrop.move_failed": "Move failed",
+  "dragdrop.overlay_title": "Drop files or folders",
+  "dragdrop.overlay_vault_zone": "Import into Vault",
+  "dragdrop.overlay_ai_zone": "Analyze with AI Assistant",
+  "upload.uploading": "Uploading {count} file(s)...",
+  "upload.success": "Successfully imported {count} file(s)",
+  "upload.partial": "Imported {count} file(s) ({errors} errors)",
+  "upload.error": "Upload failed",
   "editor.cancel": "Cancel",
   "editor.close": "Close",
   "editor.delete_error": "Delete error",
diff --git a/frontend/locales/fr.json b/frontend/locales/fr.json
index b25d1b3..32584d4 100644
--- a/frontend/locales/fr.json
+++ b/frontend/locales/fr.json
@@ -632,8 +632,15 @@
   "dashboard.views": "{count} vue(s)",
   "dashboard.welcome": "Bienvenue dans ObsiGate",
   "dashboard.zero_files": "0 fichiers",
-  "dragdrop.cross_vault_unsupported": "Cross-vault moves are not supported",
-  "dragdrop.move_failed": "Move failed",
+  "dragdrop.cross_vault_unsupported": "Le déplacement entre vaults différents n'est pas supporté",
+  "dragdrop.move_failed": "Échec du déplacement",
+  "dragdrop.overlay_title": "Déposer des fichiers ou dossiers",
+  "dragdrop.overlay_vault_zone": "Importer dans le Vault",
+  "dragdrop.overlay_ai_zone": "Analyser avec l'Assistant IA",
+  "upload.uploading": "Téléversement de {count} fichier(s)...",
+  "upload.success": "{count} fichier(s) importé(s) avec succès",
+  "upload.partial": "{count} fichier(s) importé(s) ({errors} erreurs)",
+  "upload.error": "Échec de l'importation",
   "editor.cancel": "Annuler",
   "editor.close": "Fermer",
   "editor.delete_error": "Erreur de suppression",
diff --git a/frontend/style.css b/frontend/style.css
index 0589aef..394d350 100644
--- a/frontend/style.css
+++ b/frontend/style.css
@@ -1124,6 +1124,93 @@ select {
   outline-offset: -2px;
 }
 
+/* Global Drag & Drop Overlay (#89) */
+.obsigate-drop-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 99999;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.2s cubic-bezier(0.16, 1, 0.3, 1);
+}
+
+.obsigate-drop-overlay.active {
+  opacity: 1;
+  pointer-events: auto;
+}
+
+.obsigate-drop-backdrop {
+  position: absolute;
+  inset: 0;
+  background: rgba(0, 0, 0, 0.65);
+  backdrop-filter: blur(4px);
+}
+
+.obsigate-drop-modal {
+  position: relative;
+  z-index: 1;
+  background: var(--bg-primary, #1e1e2e);
+  border: 1px solid var(--border-color, #313244);
+  border-radius: 12px;
+  padding: 24px;
+  width: min(600px, 90vw);
+  box-shadow: 0 16px 32px rgba(0, 0, 0, 0.4);
+  text-align: center;
+}
+
+.obsigate-drop-title {
+  margin: 0 0 20px 0;
+  font-size: 1.25rem;
+  font-weight: 600;
+  color: var(--text-normal, #cdd6f4);
+}
+
+.obsigate-drop-zones {
+  display: grid;
+  grid-template-columns: 1fr 1fr;
+  gap: 16px;
+}
+
+.obsigate-drop-zone {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  padding: 28px 16px;
+  border: 2px dashed var(--border-color, #45475a);
+  border-radius: 8px;
+  background: var(--bg-secondary, #181825);
+  cursor: pointer;
+  transition: all 0.15s ease;
+}
+
+.obsigate-drop-zone.hover {
+  border-color: var(--accent, #89b4fa);
+  background: color-mix(in srgb, var(--accent, #89b4fa) 15%, var(--bg-secondary, #181825));
+  transform: scale(1.02);
+}
+
+.obsigate-drop-zone-icon {
+  font-size: 2.5rem;
+  margin-bottom: 12px;
+}
+
+.obsigate-drop-zone-title {
+  font-size: 1rem;
+  font-weight: 600;
+  color: var(--text-normal, #cdd6f4);
+  margin-bottom: 6px;
+}
+
+.bookslm-composer.bookslm-drop-over {
+  outline: 2px dashed var(--accent, #89b4fa);
+  outline-offset: 2px;
+  background: color-mix(in srgb, var(--accent, #89b4fa) 10%, var(--bg-secondary, #181825));
+}
+
 .tree-children {
   padding-left: 16px;
   overflow: hidden;
diff --git a/tests/frontend/upload.test.mjs b/tests/frontend/upload.test.mjs
new file mode 100644
index 0000000..17657f9
--- /dev/null
+++ b/tests/frontend/upload.test.mjs
@@ -0,0 +1,55 @@
+/**
+ * Frontend tests for Upload & Drag-and-Drop modules (#89).
+ */
+
+import { strict as assert } from "node:assert";
+import { JSDOM } from "jsdom";
+
+// JSDOM bootstrap
+const dom = new JSDOM(`<!DOCTYPE html><html><body><div id="vault-tree"></div></body></html>`, {
+  url: "http://localhost:2020/",
+});
+const w = dom.window;
+globalThis.window = w;
+globalThis.document = w.document;
+globalThis.File = w.File;
+globalThis.FileReader = w.FileReader;
+Object.defineProperty(globalThis, "navigator", {
+  value: w.navigator,
+  configurable: true,
+  writable: true,
+});
+
+const { readDataTransferEntries } = await import("../../frontend/js/upload.js");
+
+async function runTests() {
+  console.log("Testing readDataTransferEntries empty input...");
+  const resNull = await readDataTransferEntries(null);
+  assert.deepEqual(resNull, []);
+
+  const resEmpty = await readDataTransferEntries([]);
+  assert.deepEqual(resEmpty, []);
+
+  console.log("Testing readDataTransferEntries plain files...");
+  const fakeFile1 = { name: "note1.md", webkitRelativePath: "folder/note1.md" };
+  const fakeFile2 = { name: "logo.png", webkitRelativePath: "" };
+
+  const fakeItems = [
+    { getAsFile: () => fakeFile1 },
+    { getAsFile: () => fakeFile2 },
+  ];
+
+  const results = await readDataTransferEntries(fakeItems);
+  assert.equal(results.length, 2);
+  assert.equal(results[0].path, "folder/note1.md");
+  assert.equal(results[0].isDir, false);
+  assert.equal(results[1].path, "logo.png");
+  assert.equal(results[1].isDir, false);
+
+  console.log("✅ All upload tests passed successfully!");
+}
+
+runTests().catch((err) => {
+  console.error("❌ Test failed:", err);
+  process.exit(1);
+});
diff --git a/tests/test_batch_upload.py b/tests/test_batch_upload.py
new file mode 100644
index 0000000..3dce22b
--- /dev/null
+++ b/tests/test_batch_upload.py
@@ -0,0 +1,85 @@
+"""Unit tests for batch upload and raw file saving (#89)."""
+
+import base64
+from pathlib import Path
+import pytest
+from fastapi.testclient import TestClient
+
+from backend.indexer import get_vault_data
+from backend.main import app
+from backend.services.errors import ServiceError
+from backend.services.mutations import (
+    batch_upload_files,
+    save_raw_file,
+)
+
+
+def test_save_raw_file_text_and_binary(client):
+    vault_root = Path(get_vault_data("TestVault")["path"])
+
+    # Save a markdown file
+    res = save_raw_file("TestVault", "folder/note_test.md", b"# Hello World\n")
+    assert res["success"] is True
+    assert res["path"] == "folder/note_test.md"
+    assert (vault_root / "folder" / "note_test.md").read_text(encoding="utf-8") == "# Hello World\n"
+
+    # Save a png image
+    img_bytes = b"\x89PNG\r\n\x1a\n\x00\x00\x00\rIHDR"
+    res_img = save_raw_file("TestVault", "assets/logo.png", img_bytes)
+    assert res_img["success"] is True
+    assert res_img["path"] == "assets/logo.png"
+    assert (vault_root / "assets" / "logo.png").read_bytes() == img_bytes
+
+
+def test_save_raw_file_unsupported_ext(client):
+    with pytest.raises(ServiceError) as exc_info:
+        save_raw_file("TestVault", "danger.exe", b"binary")
+    assert exc_info.value.code == "unsupported_extension"
+
+
+def test_batch_upload_files_recursive_structure(client):
+    vault_root = Path(get_vault_data("TestVault")["path"])
+
+    files = [
+        {"path": "empty_dir", "is_dir": True},
+        {"path": "doc1.md", "content": b"# Doc 1"},
+        {"path": "sub/doc2.md", "content": b"# Doc 2"},
+        {"path": "sub/deep/doc3.md", "content": b"# Doc 3"},
+        {"path": "assets/img.png", "content": b"\x89PNG\r\n\x1a\n"},
+        {"path": "invalid.exe", "content": b"bad"},
+    ]
+
+    res = batch_upload_files("TestVault", "target_folder", files, overwrite=True)
+    assert res["vault"] == "TestVault"
+    assert res["target_dir"] == "target_folder"
+    assert len(res["uploaded"]) == 4
+    assert len(res["created_dirs"]) == 1
+    assert len(res["errors"]) == 1
+    assert res["errors"][0]["path"] == "target_folder/invalid.exe"
+
+    # Verify disk files
+    assert (vault_root / "target_folder" / "empty_dir").is_dir()
+    assert (vault_root / "target_folder" / "doc1.md").read_text(encoding="utf-8") == "# Doc 1"
+    assert (vault_root / "target_folder" / "sub" / "deep" / "doc3.md").read_text(encoding="utf-8") == "# Doc 3"
+
+
+def test_api_batch_upload(client):
+    vault_root = Path(get_vault_data("TestVault")["path"])
+
+    content_b64 = base64.b64encode(b"# Uploaded via API").decode("utf-8")
+    payload = {
+        "target_dir": "api_import",
+        "files": [
+            {"path": "api_doc.md", "content": content_b64},
+            {"path": "nested/folder", "is_dir": True},
+        ],
+        "overwrite": True,
+    }
+
+    resp = client.post("/api/vault/TestVault/batch-upload", json=payload)
+    assert resp.status_code == 200
+    data = resp.json()
+    assert data["success"] is True
+    assert "api_import/api_doc.md" in data["uploaded"]
+    assert "api_import/nested/folder" in data["created_dirs"]
+    assert (vault_root / "api_import" / "api_doc.md").read_text(encoding="utf-8") == "# Uploaded via API"