Có 12 cái mới sau:

1. Output cache extensibility
2. Session state compression
3. View state mode for individual control
4. Page.MetaKeyword and Page.MetaDescription properties
5. Response.RedirectPermanent method
6. Routing in ASP.NET
7. Increase the URL character length
8. New syntax for Html Encode
9. Predictable Client IDs
10. Web.config file refactoring
11. Auto-Start ASP.NET applications
12. Improvements on Microsoft Ajax Library

Xem thêm tại đây: http://www.simple-talk.com/dotnet/asp.net/asp.net-4.0-features/