diff --git a/web/src/vocab/vocabularies-page.test.tsx b/web/src/vocab/vocabularies-page.test.tsx
new file mode 100644
index 0000000..67894d2
--- /dev/null
+++ b/web/src/vocab/vocabularies-page.test.tsx
@@ -0,0 +1,57 @@
+import { afterEach, expect, test, vi } from "vitest";
+import { screen, within } from "@testing-library/react";
+import { Route, Routes } from "react-router-dom";
+
+import { renderApp } from "../test/render";
+import { VocabulariesPage } from "./vocabularies-page";
+import { VocabularyTerms } from "./vocabulary-terms";
+import { SelectVocabularyPrompt } from "./select-vocabulary-prompt";
+
+function setViewport(wide: boolean) {
+  Object.defineProperty(window, "matchMedia", {
+    value: (query: string): MediaQueryList =>
+      ({
+        matches: wide && query === "(min-width: 1024px)",
+        media: query,
+        onchange: null,
+        addEventListener: () => {},
+        removeEventListener: () => {},
+        addListener: () => {},
+        removeListener: () => {},
+        dispatchEvent: () => false,
+      }) as MediaQueryList,
+    writable: true,
+  });
+}
+
+afterEach(() => vi.restoreAllMocks());
+
+function tree() {
+  return (
+    <Routes>
+      <Route path="/vocabularies" element={<VocabulariesPage />}>
+        <Route index element={<SelectVocabularyPrompt />} />
+        <Route path=":id" element={<VocabularyTerms />} />
+      </Route>
+    </Routes>
+  );
+}
+
+test("narrow: a selected vocabulary's detail renders in a portaled drawer", async () => {
+  setViewport(false);
+  renderApp(tree(), { route: "/vocabularies/v-material" });
+
+  const body = within(document.body);
+  expect(
+    await body.findByRole("button", { name: /close detail/i }, { timeout: 5000 }),
+  ).toBeInTheDocument();
+});
+
+test("wide: a selected vocabulary renders inline, with no detail drawer", async () => {
+  setViewport(true);
+  renderApp(tree(), { route: "/vocabularies/v-material" });
+
+  // VocabularyTerms renders its "Terms" caption inline in the right pane.
+  await screen.findByText(/terms/i);
+  expect(screen.queryByRole("button", { name: /close detail/i })).toBeNull();
+});
diff --git a/web/src/vocab/vocabularies-page.tsx b/web/src/vocab/vocabularies-page.tsx
index a82c8d1..2dfd617 100644
--- a/web/src/vocab/vocabularies-page.tsx
+++ b/web/src/vocab/vocabularies-page.tsx
@@ -1,28 +1,47 @@
-import { Outlet } from "react-router-dom";
+import { Outlet, useMatch, useNavigate } from "react-router-dom";
 import { useTranslation } from "react-i18next";
 
 import { VocabularyList } from "./vocabulary-list";
+import { DetailDrawer } from "../components/detail-drawer";
+import { useMediaQuery } from "../lib/use-media-query";
 import { useDocumentTitle } from "../lib/use-document-title";
 import { useBreadcrumb } from "../shell/use-breadcrumb";
 import { PageTitle } from "@/components/ui/page-title";
 
 export function VocabulariesPage() {
   const { t } = useTranslation();
+  const navigate = useNavigate();
+  const detailMatch = useMatch("/vocabularies/:id");
+  const open = Boolean(detailMatch);
+  const isWide = useMediaQuery("(min-width: 1024px)");
 
   useDocumentTitle(t("nav.vocabularies"));
   useBreadcrumb([{ label: t("nav.vocabularies") }]);
 
+  const close = () => navigate("/vocabularies");
+
   return (
     <div className="flex h-full flex-col">
       <PageTitle className="px-4 pt-4 pb-2">{t("nav.vocabularies")}</PageTitle>
-      <div className="grid flex-1 grid-cols-[20rem_1fr] overflow-hidden">
-        <div className="overflow-hidden border-r">
+      {isWide ? (
+        <div className="grid flex-1 grid-cols-[20rem_1fr] overflow-hidden">
+          <div className="overflow-hidden border-r">
+            <VocabularyList />
+          </div>
+          <div className="overflow-hidden">
+            <Outlet />
+          </div>
+        </div>
+      ) : (
+        <div className="flex-1 overflow-hidden">
           <VocabularyList />
         </div>
-        <div className="overflow-hidden">
+      )}
+      {!isWide && open && (
+        <DetailDrawer open={open} onClose={close} ariaLabel={t("vocab.terms")}>
           <Outlet />
-        </div>
-      </div>
+        </DetailDrawer>
+      )}
     </div>
   );
 }