For several years, I use TDD (Test-Driven Development) to produce code. I no longer plans to work without using TDD. The use of TDD significantly increases code quality, but does not guarantee that the code is the code that corresponds to the requirements specifications (write the "right code" with BDD as opposed to the write "code right" with BDD).

Dan North has described in an article in published in 2006 the foundations of the BDD (Behavior-Driven Development). In this article, he introduces the formalism "When Given Then". This formalism is used in all tools dedicated to BDD.

This is a short list of open source BDD tools that you can use with .Net :

• SpecFlow: Here you can find an article in MSDN Magazine and 2 webcasts (http://channel9.msdn.com/posts/ASPNET-MVC-With-Community-Tools-Part-2-Spec-Flow-and-WatiN and http://channel9.msdn.com/posts/ASPNET-MVC-With-Community-Tools-Part-3-More-Spec-Flow-and-WatiN) published on Chanel9.
• NSpec: This is certainly the most used project. There are many examples on the web.
• StoryQ: This project is hosted on Codeplex. This small project is very simple to implement and very useful.