As I mentioned here, I have been digging into what's out there for WPF LOB applications. It's been a long time since I've kept up with the work the patterns & practices group has produced. One of the things I've seen a webcast/blog post or two about is the Validation Application Block. They have put together a nice approach that allows you to define validation once on your business entities. In addition, the block includes adapters that allow you to surface the validation in ASP.NET, Windows Forms, and the Windows Communications Framework (WCF). In theory, the block can be used with WPF as well, but an adapter hasn't been built. I came across two solutions. The first one, Validation Application Block, meet WPF, I found on Tom Hollander's blog. The other, came from one of the EntLib Contrib projects on CodePlex. The project is called Standalone Validation Block. It's two gems in one! First, it allows you to use the core validation framework without having to take a dependency on the full Enterprise Library. Second, it has a solution for surfacing the validation in your WPF UI. Go check it out!