diff --git a/surfsense_backend/app/routes/export_routes.py b/surfsense_backend/app/routes/export_routes.py
index 0bc5b4d1c..641c7fedb 100644
--- a/surfsense_backend/app/routes/export_routes.py
+++ b/surfsense_backend/app/routes/export_routes.py
@@ -1,11 +1,14 @@
 """Routes for exporting knowledge base content as ZIP."""
 
 import logging
+import os
 
-from fastapi import APIRouter, Depends, Query
+from fastapi import APIRouter, Depends, HTTPException, Query
+from fastapi.responses import StreamingResponse
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.db import Permission, User, get_async_session
+from app.services.export_service import build_export_zip
 from app.users import current_active_user
 from app.utils.rbac import check_permission
 
@@ -21,11 +24,7 @@ async def export_knowledge_base(
     session: AsyncSession = Depends(get_async_session),
     user: User = Depends(current_active_user),
 ):
-    """Export documents as a ZIP of markdown files preserving folder structure.
-
-    If folder_id is provided, only that folder's subtree is exported.
-    Otherwise, the entire search space is exported.
-    """
+    """Export documents as a ZIP of markdown files preserving folder structure."""
     await check_permission(
         session,
         user,
@@ -34,5 +33,29 @@ async def export_knowledge_base(
         "You don't have permission to export documents in this search space",
     )
 
-    # TODO: implement export logic
-    return {"message": "Export endpoint placeholder"}
+    try:
+        result = await build_export_zip(session, search_space_id, folder_id)
+    except ValueError as e:
+        raise HTTPException(status_code=404, detail=str(e)) from None
+
+    def stream_and_cleanup():
+        try:
+            with open(result.zip_path, "rb") as f:
+                while chunk := f.read(8192):
+                    yield chunk
+        finally:
+            os.unlink(result.zip_path)
+
+    headers = {
+        "Content-Disposition": f'attachment; filename="{result.export_name}.zip"',
+        "Content-Length": str(result.zip_size),
+    }
+
+    if result.skipped_docs:
+        headers["X-Skipped-Documents"] = str(len(result.skipped_docs))
+
+    return StreamingResponse(
+        stream_and_cleanup(),
+        media_type="application/zip",
+        headers=headers,
+    )
diff --git a/surfsense_backend/app/services/export_service.py b/surfsense_backend/app/services/export_service.py
new file mode 100644
index 000000000..49f1a127a
--- /dev/null
+++ b/surfsense_backend/app/services/export_service.py
@@ -0,0 +1,168 @@
+"""Service for exporting knowledge base content as a ZIP archive."""
+
+import logging
+import os
+import tempfile
+import zipfile
+from dataclasses import dataclass, field
+
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.future import select
+
+from app.db import Chunk, Document, Folder
+from app.services.folder_service import get_folder_subtree_ids
+
+logger = logging.getLogger(__name__)
+
+
+def _sanitize_filename(title: str) -> str:
+    safe = "".join(c if c.isalnum() or c in " -_." else "_" for c in title).strip()
+    return safe[:80] or "document"
+
+
+def _build_folder_path_map(folders: list[Folder]) -> dict[int, str]:
+    """Build a mapping of folder_id -> full path string (e.g. 'Research/AI')."""
+    id_to_folder = {f.id: f for f in folders}
+    cache: dict[int, str] = {}
+
+    def resolve(folder_id: int) -> str:
+        if folder_id in cache:
+            return cache[folder_id]
+        folder = id_to_folder[folder_id]
+        if folder.parent_id is None or folder.parent_id not in id_to_folder:
+            cache[folder_id] = folder.name
+        else:
+            cache[folder_id] = f"{resolve(folder.parent_id)}/{folder.name}"
+        return cache[folder_id]
+
+    for f in folders:
+        resolve(f.id)
+
+    return cache
+
+
+async def _get_document_markdown(
+    session: AsyncSession, document: Document
+) -> str | None:
+    """Resolve markdown content using the 3-tier fallback:
+    1. source_markdown  2. blocknote_document conversion  3. chunk concatenation
+    """
+    if document.source_markdown is not None:
+        return document.source_markdown
+
+    if document.blocknote_document:
+        from app.utils.blocknote_to_markdown import blocknote_to_markdown
+
+        md = blocknote_to_markdown(document.blocknote_document)
+        if md:
+            return md
+
+    chunk_result = await session.execute(
+        select(Chunk.content)
+        .filter(Chunk.document_id == document.id)
+        .order_by(Chunk.id)
+    )
+    chunks = chunk_result.scalars().all()
+    if chunks:
+        return "\n\n".join(chunks)
+
+    return None
+
+
+@dataclass
+class ExportResult:
+    zip_path: str
+    export_name: str
+    zip_size: int
+    skipped_docs: list[str] = field(default_factory=list)
+
+
+async def build_export_zip(
+    session: AsyncSession,
+    search_space_id: int,
+    folder_id: int | None = None,
+) -> ExportResult:
+    """Build a ZIP archive of markdown documents preserving folder structure.
+
+    Returns an ExportResult with the path to the temp ZIP file.
+    The caller is responsible for streaming and cleaning up the file.
+
+    Raises ValueError if folder_id is provided but not found.
+    """
+    if folder_id is not None:
+        folder = await session.get(Folder, folder_id)
+        if not folder or folder.search_space_id != search_space_id:
+            raise ValueError("Folder not found")
+        target_folder_ids = set(await get_folder_subtree_ids(session, folder_id))
+    else:
+        target_folder_ids = None
+
+    folder_query = select(Folder).where(Folder.search_space_id == search_space_id)
+    if target_folder_ids is not None:
+        folder_query = folder_query.where(Folder.id.in_(target_folder_ids))
+    folder_result = await session.execute(folder_query)
+    folders = list(folder_result.scalars().all())
+
+    folder_path_map = _build_folder_path_map(folders)
+
+    doc_query = select(Document).where(Document.search_space_id == search_space_id)
+    if target_folder_ids is not None:
+        doc_query = doc_query.where(Document.folder_id.in_(target_folder_ids))
+    doc_result = await session.execute(doc_query)
+    documents = list(doc_result.scalars().all())
+
+    fd, tmp_path = tempfile.mkstemp(suffix=".zip")
+    os.close(fd)
+
+    try:
+        used_paths: dict[str, int] = {}
+        skipped_docs: list[str] = []
+
+        with zipfile.ZipFile(tmp_path, "w", zipfile.ZIP_DEFLATED) as zf:
+            for doc in documents:
+                status = doc.status or {}
+                state = status.get("state", "ready") if isinstance(status, dict) else "ready"
+                if state in ("pending", "processing"):
+                    skipped_docs.append(doc.title or "Untitled")
+                    continue
+
+                markdown = await _get_document_markdown(session, doc)
+                if not markdown or not markdown.strip():
+                    continue
+
+                if doc.folder_id and doc.folder_id in folder_path_map:
+                    dir_path = folder_path_map[doc.folder_id]
+                else:
+                    dir_path = ""
+
+                base_name = _sanitize_filename(doc.title or "Untitled")
+                file_path = f"{dir_path}/{base_name}.md" if dir_path else f"{base_name}.md"
+
+                if file_path in used_paths:
+                    used_paths[file_path] += 1
+                    suffix = used_paths[file_path]
+                    file_path = (
+                        f"{dir_path}/{base_name}_{suffix}.md"
+                        if dir_path
+                        else f"{base_name}_{suffix}.md"
+                    )
+                else:
+                    used_paths[file_path] = 1
+
+                zf.writestr(file_path, markdown)
+
+        export_name = "knowledge-base"
+        if folder_id is not None and folder_id in folder_path_map:
+            export_name = _sanitize_filename(folder_path_map[folder_id].split("/")[0])
+
+        return ExportResult(
+            zip_path=tmp_path,
+            export_name=export_name,
+            zip_size=os.path.getsize(tmp_path),
+            skipped_docs=skipped_docs,
+        )
+
+    except Exception:
+        if os.path.exists(tmp_path):
+            os.unlink(tmp_path)
+        raise