diff --git a/src/App.tsx b/src/App.tsx
index e755869..eeae0c6 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1,5 +1,6 @@
 import { Route, Routes } from 'react-router-dom'
 import { PageLayout } from './components/layout/PageLayout'
+import { ErrorPage } from './components/shared/ErrorPage'
 import { HomePage } from './pages/HomePage'
 import { ProfilePage } from './pages/ProfilePage'
 import { RepoPage } from './pages/RepoPage'
@@ -13,6 +14,12 @@ function App() {
         <Route path=":handle" element={<ProfilePage />} />
         <Route path=":handle/:repo" element={<RepoPage />} />
         <Route path="strings/:handle/:string" element={<StringPage />} />
+        <Route
+          path="*"
+          element={
+            <ErrorPage title="Page not found" message="This address doesn't point to a page." />
+          }
+        />
       </Routes>
     </PageLayout>
   )
diff --git a/src/components/shared/ErrorPage.tsx b/src/components/shared/ErrorPage.tsx
new file mode 100644
index 0000000..7e5134e
--- /dev/null
+++ b/src/components/shared/ErrorPage.tsx
@@ -0,0 +1,37 @@
+import { Link } from 'react-router-dom'
+import { PageContainer } from '../layout/PageContainer'
+import { SurfaceCard } from './SurfaceCard'
+
+type ErrorPageProps = {
+  title: string
+  message: string
+  details?: string
+}
+
+export function ErrorPage({ title, message, details }: ErrorPageProps) {
+  return (
+    <main>
+      <PageContainer className="flex min-h-[calc(100vh-12rem)] items-center justify-center py-8">
+        <section className="w-full max-w-xl" role="alert">
+          <SurfaceCard className="p-8 text-center">
+            <h1 className="font-mono text-2xl text-ctp-text">{title}</h1>
+            <p className="mt-3">{message}</p>
+
+            {details !== undefined && (
+              <details className="mt-5 rounded border border-ctp-surface-1 bg-ctp-crust p-3 text-left text-sm">
+                <summary className="cursor-pointer font-mono text-ctp-subtext-0">
+                  Technical details
+                </summary>
+                <p className="mt-3 break-words font-mono text-xs text-ctp-subtext-1">{details}</p>
+              </details>
+            )}
+
+            <Link to="/" className="mt-6 inline-block font-mono text-sm">
+              Go home
+            </Link>
+          </SurfaceCard>
+        </section>
+      </PageContainer>
+    </main>
+  )
+}
diff --git a/src/pages/ProfilePage.tsx b/src/pages/ProfilePage.tsx
index bc8d4c3..6676236 100644
--- a/src/pages/ProfilePage.tsx
+++ b/src/pages/ProfilePage.tsx
@@ -6,6 +6,7 @@ import { ProfileHeader } from '../components/profile/ProfileHeader'
 import { ProfileSection } from '../components/profile/ProfileSection'
 import { ProfileTabs } from '../components/profile/ProfileTabs'
 import { RepoListItem } from '../components/repo/RepoListItem'
+import { ErrorPage } from '../components/shared/ErrorPage'
 import { StringListItem } from '../components/string/StringListItem'
 import { VouchList } from '../components/vouch/VouchList'
 import { useProfilePage } from '../hooks/useProfilePage'
@@ -21,11 +22,17 @@ export function ProfilePage() {
   const { pageData, error } = useProfilePage(handle)
 
   if (handle === null) {
-    return <p>Invalid handle</p>
+    return <ErrorPage title="Profile not found" message="That profile address is not valid." />
   }
 
   if (error) {
-    return <p role="alert">Could not load profile: {error.message}</p>
+    return (
+      <ErrorPage
+        title="We couldn't load this profile"
+        message="The profile may not exist, or the service may be temporarily unavailable."
+        details={error.message}
+      />
+    )
   }
 
   if (pageData === null) {
diff --git a/src/pages/RepoPage.tsx b/src/pages/RepoPage.tsx
index e505516..65b69de 100644
--- a/src/pages/RepoPage.tsx
+++ b/src/pages/RepoPage.tsx
@@ -10,6 +10,7 @@ import { RepoTabs } from '../components/repo/RepoTabs'
 import { RepoView } from '../components/repo/RepoView'
 import { RepoWorkspace } from '../components/repo/RepoWorkspace'
 import { RepoPageSkeleton } from '../components/shared/PageSkeletons'
+import { ErrorPage } from '../components/shared/ErrorPage'
 import { SurfaceCard } from '../components/shared/SurfaceCard'
 import { useRepoPage } from '../hooks/useRepoPage'
 import { parseHandle } from '../lib/routes'
@@ -34,11 +35,19 @@ export function RepoPage() {
   }, [requestedSection, pageData])
 
   if (handle === null || routeRepo === undefined) {
-    return <p>Invalid repository route</p>
+    return (
+      <ErrorPage title="Repository not found" message="That repository address is not valid." />
+    )
   }
 
   if (error) {
-    return <p role="alert">Could not load repository: {error.message}</p>
+    return (
+      <ErrorPage
+        title="We couldn't load this repository"
+        message="The repository may not exist, or the service may be temporarily unavailable."
+        details={error.message}
+      />
+    )
   }
 
   if (pageData === null) {
diff --git a/src/pages/StringPage.tsx b/src/pages/StringPage.tsx
index 18111fd..9e0d519 100644
--- a/src/pages/StringPage.tsx
+++ b/src/pages/StringPage.tsx
@@ -1,6 +1,7 @@
 import { useParams } from 'react-router-dom'
 import { ProfileByline } from '../components/profile/ProfileByline'
 import { ProfilePageSkeleton } from '../components/shared/PageSkeletons'
+import { ErrorPage } from '../components/shared/ErrorPage'
 import { StringView } from '../components/string/StringView'
 import { useStringPage } from '../hooks/useStringPage'
 import { parseHandle } from '../lib/routes'
@@ -11,11 +12,17 @@ export function StringPage() {
   const { pageData, error } = useStringPage(handle, routeString)
 
   if (handle === null || routeString === undefined) {
-    return <p>Invalid string route</p>
+    return <ErrorPage title="String not found" message="That string address is not valid." />
   }
 
   if (error) {
-    return <p role="alert">Could not load string: {error.message}</p>
+    return (
+      <ErrorPage
+        title="We couldn't load this string"
+        message="The string may not exist, or the service may be temporarily unavailable."
+        details={error.message}
+      />
+    )
   }
 
   if (pageData === null) {