The idea of creating rich interactivity without code should sound very appearing to designers, because we want to turn static UI into interactive prototypes and test out our design ideas quickly. In Blend 3, “Behaviors” are packaged, re-usable building blocks of interactivity. They can be visually applied to UI components in the application using drag and drop. No more opening up Visual Studio and writing routine code like starting an animation when a button is clicked. Blend 3 will have bunch of commonly used Behaviors shipping with the tool, but they are extensible so that you or your developers can create your customized Behaviors.