Server-side rendering (SSR) allows your Web API to generate HTML content on the server and send it to the client, reducing the initial page load time and improving SEO. In ASP.NET Core, you can implement SSR by using server-side rendering frameworks like ReactJS.NET or Angular Universal. These frameworks enable you to render React or Angular components on the server and send the generated HTML to the client. By combining the power of server-side rendering with client-side interactivity, you can create fast and SEO-friendly web applications with ASP.NET Core.