App Router is Next.js's modern routing system that uses your folder structure to create routes automatically.

It replaces the older Pages Router and brings React Server Components, which means you can fetch data and render on the server by default without extra setup.

Most builders use it for new Next.js projects because it handles layouts, loading states, and nested routes more cleanly than the old approach. You create an app directory, add folders for routes, and drop in page.js files.

Ships with Next.js 13+. The learning curve is real if you're coming from Pages Router, but the performance gains and simpler data fetching make it worth the switch.