.NET 4 ships with a new and much improved version of Entity Framework (EF) - a data access and OR/M library that lives within the System.Data.Entity namespace.
When Entity Framework was first introduced with .NET 3.5 SP1, developers provided a lot of feedback on things they thought were missing or incomplete with that first release. The SQL team did a good job of listening to this feedback, and really focused the EF that ships with .NET 4 on addressing it. Some of the big improvements in EF4 include:
POCO Support: You can now define entities without requiring base classes or data persistence attributes. Lazy Loading Support: You can now load sub-objects of a model on demand instead of loading them up front. N-Tier Support and Self-Tracking Entities: Handle scenarios where entities flow across tiers or stateless web calls. Go to the complete details ...