React Server Components (RSC) have changed how we think about rendering and data in React apps. If you're using Next.js 13 or later with the App Router, you're already using them by default—so it's worth understanding what they do and why they matter.
What Are Server Components?
In the traditional model, most of your React code runs in the browser. With Server Components, a portion of your component tree runs only on the server. They never ship their JavaScript to the client, which means smaller bundles and faster initial loads. They're great for fetching data, reading from a database, or using server-only libraries without exposing them to the client.
How They Differ from Server-Side Rendering
SSR still sends HTML and then “hydrates” the page with client-side JavaScript. Server Components go further: they produce a special format that the client can stream and compose with Client Components. So you get the benefit of server-only logic (no secrets in the bundle, direct DB access) while keeping interactivity where you need it with "use client".
When to Use Client vs Server
Use Server Components for layout, static content, and data fetching. Use Client Components when you need state, event handlers, or browser APIs. The boundary is clear: add "use client" at the top of a file when that component (and its children) need to run on the client. Everything else stays on the server by default.
Performance and DX Benefits
Because Server Components don't ship JS, your client bundle stays smaller. You can also fetch data right inside components without extra API routes or getServerSideProps—no waterfall requests. For Next.js apps, this means faster Time to First Byte and a smoother experience as content streams in.
Summary
React Server Components are a core part of the Next.js App Router. They help you build faster, lighter apps by keeping heavy logic and data on the server and sending only what's needed to the client. Once you get the mental model of server vs client boundaries, they become a natural part of how you structure your app.