Constrasting WPF with Silverlight
Silverlight is a platform for developing Rich Internet Applications (RIA), whereas WPF is primarily intended for desktop applications. Silverlight is a direct competitor to Adobe Flash and it has a strong focus on media, cross-platform compatibility, as well as a small download and install footprint. Like Flash, Silverlight applications are hosted in a browser.
Microsoft has intentionally designed Silverlight to be very similar to WPF, although the two are separate products. In fact, an early name for Silverlight was WPF/E or Windows Presentation Foundation/Everywhere. Developers familiar with one technology will have a head start with the other.