diff --git a/backend/src/routes/projects.ts b/backend/src/routes/projects.ts
index 58de3c0..38e38b2 100644
--- a/backend/src/routes/projects.ts
+++ b/backend/src/routes/projects.ts
@@ -83,6 +83,7 @@ projectsRouter.get("/", requireAuth, async (req, res) => {
 // POST /projects
 projectsRouter.post("/", requireAuth, async (req, res) => {
   const userId = res.locals.userId as string;
+  const userEmail = res.locals.userEmail as string | undefined;
   const { name, cm_number, shared_with } = req.body as {
     name: string;
     cm_number?: string;
@@ -90,6 +91,23 @@ projectsRouter.post("/", requireAuth, async (req, res) => {
   };
   if (!name?.trim())
     return void res.status(400).json({ detail: "name is required" });
+  const normalizedUserEmail = userEmail?.trim().toLowerCase();
+  const cleanedSharedWith: string[] = [];
+  const seenSharedEmails = new Set<string>();
+  if (Array.isArray(shared_with)) {
+    for (const raw of shared_with) {
+      if (typeof raw !== "string") continue;
+      const e = raw.trim().toLowerCase();
+      if (!e || seenSharedEmails.has(e)) continue;
+      if (normalizedUserEmail && e === normalizedUserEmail) {
+        return void res
+          .status(400)
+          .json({ detail: "You cannot share a project with yourself." });
+      }
+      seenSharedEmails.add(e);
+      cleanedSharedWith.push(e);
+    }
+  }
 
   const db = createServerSupabase();
   const { data, error } = await db
@@ -98,7 +116,7 @@ projectsRouter.post("/", requireAuth, async (req, res) => {
       user_id: userId,
       name: name.trim(),
       cm_number: cm_number ?? null,
-      shared_with: shared_with ?? [],
+      shared_with: cleanedSharedWith,
     })
     .select("*")
     .single();
@@ -238,18 +256,25 @@ projectsRouter.get("/:projectId/people", requireAuth, async (req, res) => {
 // PATCH /projects/:projectId
 projectsRouter.patch("/:projectId", requireAuth, async (req, res) => {
   const userId = res.locals.userId as string;
+  const userEmail = res.locals.userEmail as string | undefined;
   const { projectId } = req.params;
   const updates: Record<string, unknown> = {};
   if (req.body.name != null) updates.name = req.body.name;
   if (req.body.cm_number != null) updates.cm_number = req.body.cm_number;
   if (Array.isArray(req.body.shared_with)) {
     // Normalise: lowercase + dedupe + drop empties.
+    const normalizedUserEmail = userEmail?.trim().toLowerCase();
     const seen = new Set<string>();
     const cleaned: string[] = [];
     for (const raw of req.body.shared_with) {
       if (typeof raw !== "string") continue;
       const e = raw.trim().toLowerCase();
       if (!e || seen.has(e)) continue;
+      if (normalizedUserEmail && e === normalizedUserEmail) {
+        return void res
+          .status(400)
+          .json({ detail: "You cannot share a project with yourself." });
+      }
       seen.add(e);
       cleaned.push(e);
     }
diff --git a/backend/src/routes/tabular.ts b/backend/src/routes/tabular.ts
index b7efff6..e73454d 100644
--- a/backend/src/routes/tabular.ts
+++ b/backend/src/routes/tabular.ts
@@ -463,12 +463,18 @@ tabularRouter.patch("/:reviewId", requireAuth, async (req, res) => {
     // making the call. Normalize lowercase + dedupe + drop empties.
     let sharedWithUpdate: string[] | undefined;
     if (Array.isArray(req.body.shared_with)) {
+        const normalizedUserEmail = userEmail?.trim().toLowerCase();
         const seen = new Set<string>();
         const cleaned: string[] = [];
         for (const raw of req.body.shared_with) {
             if (typeof raw !== "string") continue;
             const e = raw.trim().toLowerCase();
             if (!e || seen.has(e)) continue;
+            if (normalizedUserEmail && e === normalizedUserEmail) {
+                return void res.status(400).json({
+                    detail: "You cannot share a tabular review with yourself.",
+                });
+            }
             seen.add(e);
             cleaned.push(e);
         }
diff --git a/frontend/src/app/components/projects/NewProjectModal.tsx b/frontend/src/app/components/projects/NewProjectModal.tsx
index 7cc5c80..1c3b39d 100644
--- a/frontend/src/app/components/projects/NewProjectModal.tsx
+++ b/frontend/src/app/components/projects/NewProjectModal.tsx
@@ -11,6 +11,7 @@ import { useDirectoryData } from "../shared/useDirectoryData";
 import { FileDirectory } from "../shared/FileDirectory";
 import { EmailPillInput } from "../shared/EmailPillInput";
 import type { MikeProject } from "../shared/types";
+import { useAuth } from "@/contexts/AuthContext";
 
 interface Props {
     open: boolean;
@@ -28,6 +29,8 @@ export function NewProjectModal({ open, onClose, onCreated }: Props) {
     const [loading, setLoading] = useState(false);
     const [error, setError] = useState("");
     const fileInputRef = useRef<HTMLInputElement>(null);
+    const { user } = useAuth();
+    const ownEmail = user?.email?.trim().toLowerCase() ?? null;
 
     const { loading: dirLoading, standaloneDocuments, projects: dirProjects } = useDirectoryData(open);
 
@@ -49,7 +52,9 @@ export function NewProjectModal({ open, onClose, onCreated }: Props) {
             const project = await createProject(
                 name.trim(),
                 cmNumber.trim() || undefined,
-                sharedEmails,
+                ownEmail
+                    ? sharedEmails.filter((email) => email !== ownEmail)
+                    : sharedEmails,
             );
             await Promise.all([
                 ...[...selectedDocIds].map((id) => addDocumentToProject(project.id, id).catch(() => {})),
@@ -137,6 +142,11 @@ export function NewProjectModal({ open, onClose, onCreated }: Props) {
                                 <EmailPillInput
                                     emails={sharedEmails}
                                     onChange={setSharedEmails}
+                                    validate={async (email) =>
+                                        ownEmail && email === ownEmail
+                                            ? "You cannot share a project with yourself."
+                                            : null
+                                    }
                                     placeholder="Add colleagues by email…"
                                 />
                             </div>
diff --git a/frontend/src/app/components/shared/PeopleModal.tsx b/frontend/src/app/components/shared/PeopleModal.tsx
index ce02d1c..8a70d39 100644
--- a/frontend/src/app/components/shared/PeopleModal.tsx
+++ b/frontend/src/app/components/shared/PeopleModal.tsx
@@ -136,13 +136,22 @@ export function PeopleModal({
     }
 
     const trimmedNewEmail = newEmail.trim().toLowerCase();
+    const normalizedCurrentUserEmail =
+        currentUserEmail?.trim().toLowerCase() ?? null;
     const isValidEmail = EMAIL_RE.test(trimmedNewEmail);
     const sharedLower = sharedWith.map((e) => e.toLowerCase());
     const alreadyShared = sharedLower.includes(trimmedNewEmail);
     const isOwnerEmail =
         !!ownerEmail && trimmedNewEmail === ownerEmail.toLowerCase();
+    const isSelfEmail =
+        !!normalizedCurrentUserEmail &&
+        trimmedNewEmail === normalizedCurrentUserEmail;
     const canAdd =
-        isValidEmail && !alreadyShared && !isOwnerEmail && busy === null;
+        isValidEmail &&
+        !alreadyShared &&
+        !isOwnerEmail &&
+        !isSelfEmail &&
+        busy === null;
 
     async function handleAdd() {
         if (!canAdd || !onSharedWithChange) return;
@@ -249,10 +258,16 @@ export function PeopleModal({
                                 {trimmedNewEmail} is the owner.
                             </p>
                         )}
+                        {isSelfEmail && !isOwnerEmail && trimmedNewEmail && (
+                            <p className="mt-1.5 text-xs text-gray-400">
+                                You cannot share this with yourself.
+                            </p>
+                        )}
                         {trimmedNewEmail &&
                             !isValidEmail &&
                             !alreadyShared &&
-                            !isOwnerEmail && (
+                            !isOwnerEmail &&
+                            !isSelfEmail && (
                                 <p className="mt-1.5 text-xs text-gray-400">
                                     Enter a valid email.
                                 </p>