Streaming SSR (Streaming Server-Side Rendering) is a rendering technique in which the server sends HTML to the browser in chunks as it is generated rather than waiting for the entire page to be ready before transmitting the response. By using HTTP chunked transfer encoding or HTTP/2 server push, the browser can begin parsing and rendering the initial HTML — including the document head, critical CSS, and above-the-fold content — while the server is still generating the rest of the page, such as data-dependent sections. This reduces Time to First Byte for the first meaningful content and can significantly improve First Contentful Paint and Largest Contentful Paint. React 18, released in March 2022, introduced first-class streaming SSR support via renderToPipeableStream and the <Suspense> API, which allows components to stream independently as their data resolves. Next.js App Router (launched 2023) and Remix both build on React 18’s streaming primitives. Streaming is particularly beneficial for pages with slow database queries or external API calls that would otherwise block the entire response.