diff --git a/.changeset/stale-peas-lay.md b/.changeset/stale-peas-lay.md
new file mode 100644
index 000000000..4243f5750
--- /dev/null
+++ b/.changeset/stale-peas-lay.md
@@ -0,0 +1,6 @@
+---
+'@myst-theme/site': patch
+'@myst-theme/book': patch
+---
+
+Add project.parts.primary_sidebar_footer option
diff --git a/.gitignore b/.gitignore
index 17213c01f..23db67ffd 100644
--- a/.gitignore
+++ b/.gitignore
@@ -38,4 +38,4 @@ _build
 
 # yalc
 .yalc
-yalc.lock
+yalc.lock
\ No newline at end of file
diff --git a/docs/_site/primary_sidebar_footer.md b/docs/_site/primary_sidebar_footer.md
new file mode 100644
index 000000000..73b1b844f
--- /dev/null
+++ b/docs/_site/primary_sidebar_footer.md
@@ -0,0 +1 @@
+**Custom Footer** | [GitHub](https://github.com/jupyter-book/myst-theme)
diff --git a/docs/myst.yml b/docs/myst.yml
index faa42af0e..a6da43f56 100644
--- a/docs/myst.yml
+++ b/docs/myst.yml
@@ -11,6 +11,7 @@ project:
   parts:
     banner: _site/banner.md
     footer: _site/footer.md
+    primary_sidebar_footer: _site/primary_sidebar_footer.md
   toc:
     - file: index.md
     - file: examples.md
diff --git a/docs/ui.md b/docs/ui.md
index 5669df1b1..11aa0eabd 100644
--- a/docs/ui.md
+++ b/docs/ui.md
@@ -42,3 +42,23 @@ project:
 
 - Appears at the bottom of every page
 - Supports any MyST markdown content (links, formatting, etc.)
+
+## Sidebar Footer
+
+Display custom content at the bottom of the primary sidebar (table of contents).
+
+### Configuration
+
+Create a markdown file with your sidebar footer content and add it to `myst.yml`:
+
+```yaml
+project:
+  parts:
+    primary_sidebar_footer: _site/primary_sidebar_footer.md
+```
+
+### Behavior
+
+- Appears at the bottom of the primary sidebar (left-side navigation)
+- If the `.md` file it points to is empty, the footer will not be visible
+- If not configured, falls back to the default "Made with MyST" footer
diff --git a/themes/book/app/components/SidebarFooter.tsx b/themes/book/app/components/SidebarFooter.tsx
new file mode 100644
index 000000000..995edd849
--- /dev/null
+++ b/themes/book/app/components/SidebarFooter.tsx
@@ -0,0 +1,15 @@
+import type { GenericParent } from 'myst-common';
+import { MyST } from 'myst-to-react';
+import { MadeWithMyst } from '@myst-theme/icons';
+
+export function SidebarFooter({ content }: { content?: GenericParent }) {
+  if (!content) {
+    return <MadeWithMyst />;
+  }
+
+  return (
+    <div className="article footer myst-primary-sidebar-footer">
+      <MyST ast={content} />
+    </div>
+  );
+}
diff --git a/themes/book/app/routes/$.tsx b/themes/book/app/routes/$.tsx
index e81ad1803..e0a20c67c 100644
--- a/themes/book/app/routes/$.tsx
+++ b/themes/book/app/routes/$.tsx
@@ -31,6 +31,7 @@ import { MadeWithMyst } from '@myst-theme/icons';
 import { ArticlePage } from '../components/ArticlePage.js';
 import { Footer } from '../components/Footer.js';
 import { Banner } from '../components/Banner.js';
+import { SidebarFooter } from '../components/SidebarFooter.js';
 import type { TemplateOptions } from '../types.js';
 import { useRouteError, isRouteErrorResponse } from '@remix-run/react';
 type ManifestProject = Required<SiteManifest>['projects'][0];
@@ -102,7 +103,7 @@ function ArticlePageAndNavigationInternal({
       <PrimaryNavigation
         sidebarRef={toc}
         hide_toc={hide_toc}
-        footer={<MadeWithMyst />}
+        footer={<SidebarFooter content={projectParts?.primary_sidebar_footer?.mdast} />}
         projectSlug={projectSlug}
       />
       <TabStateProvider>
diff --git a/themes/book/template.yml b/themes/book/template.yml
index ebfefd20e..ae8fd8f24 100644
--- a/themes/book/template.yml
+++ b/themes/book/template.yml
@@ -74,6 +74,9 @@ parts:
   - id: footer
     description: The site wide footer
     required: false
+  - id: primary_sidebar_footer
+    description: The primary sidebar footer, to replace Made with MyST
+    required: false
 build:
   install: npm install
   start: npm run start