React Server Actions: Server Mutations From Client Components

**React Server Actions** are async functions marked with `"use server"` that run on the server but can be invoked from Client Components, often via forms. They stabilized in **React 19** with integration in Next.js App Router and other frameworks.

HTML `<form action={serverAction}>` works without JavaScript (progressive enhancement). Frameworks serialize arguments and enforce origin checks to reduce CSRF risk; still validate auth inside every action.

Use actions for mutations (create, update, delete), not bulk data reads better served by Server Components. Revalidate caches or paths after mutations per framework APIs (`revalidatePath` in Next.js).

Read react.dev reference and your framework's security guide. Never trust client-supplied IDs without server-side authorization checks.