With Microsoft Expression Blend 4, you can create websites and applications based on Microsoft Silverlight 3 and Microsoft Silverlight 4, and desktop applications based on Windows Presentation Foundation (WPF) 3.5 with Service Pack 1 (SP1) and WPF4.

Expression Blend provides new support for prototyping, interactivity through behaviors, special Silverlight functionality, and on-the-fly sample data generation. Expression Blend includes new behaviors that are quickly and easily configured

Expression Blend offers new sample data, behaviors, and features of project templates to support the Model-View-ViewModel (MVVM) pattern

The MVVM pattern is a way to structure a Silverlight or WPF application so that user interface (UI) objects are as decoupled as possible from the application's data and behavior. This makes it easier for design tasks and development tasks to be performed independently and without breaking each other. Essentially, your UI is the View. You bind objects in the View to properties and commands of the ViewModel, and the View can also call methods on the ViewModel.

Compatible with Silverlight 3 and WPF 3.5 with Service Pack 1 (SP1)

Interoperate able with Visual Studio.

Included New Shapes: The Assets panel in Expression Blend contains a new Shapes category, including presets for the easy creation of arcs, arrows, callouts, and polygons.

New Controls: Expression Blend has tooling support for the RichTextBox control in Silverlight.

XAML cleanliness :Expression Blend generates less XAML with respect to animations and animation-related properties.

MVVM project template: Expression Blend includes a new project template that offers a basic starting point for Model-View-ViewModel pattern applications.

Run project with CTRL+F5:To improve consistency with Visual Studio, you can now invoke the Run Project command by pressing either CTRL+F5 or F5