What is the difference between the Windows Presentation Foundation (WPF) and Silverlight

What is the difference between the Windows Presentation Foundation (WPF) and Silverlight, and in what scenarios does it make sense to use each? 

Microsoft feels that user experience is important, and invested in multiple technologies to promote better user experience.  Both WPF and Silverlight use XAML (Extensible Application Markup Language) under the covers. 

Let's look at some of the different characteristics of each technology:

WPF:

• Ships as part of the .NET Framework (version 3.0 and onward)
• Runs as Windows application or as web "browser application" (called XBAP, for "XAML Browser Application").  Note that XBAPs run only in Internet Explorer with .NET 3.0 and in both Internet Explorer and Firefox with .NET 3.5.  
• Runs on Windows machines only (Windows XP, Windows Server 2003, Windows Vista, and Windows Server 2008)
• Richest functionality, including 3D graphics

Silverlight:

• Ships independently
• Runs in web browsers only (Internet Explorer, Firefox, Safari)
• Runs on Windows or Mac operating systems (also on Linux via Moonlight, which is an open source implementation of Silverlight based on Mono)
• Functionality is a subset of WPF's feature set