The document compares ASP.NET MVC 3 and ASP.NET MVC 4 across 12 categories. Some key differences include: - Bundling and minification, display modes, and custom controller locations are only supported in MVC 4. - The empty project template is truly empty in MVC 4, unlike MVC 3. - Features like WebSockets, SignalR, recipes, mobile project templates, and Web API are new to MVC 4. - Asynchronous controller implementation is simpler using async/await in MVC 4 versus AsyncController in MVC 3. - MVC 4 has better support for Azure, Facebook/Twitter authentication, and various new project templates.