http://bhaidar.net/cs/archive/2009/05/01/internal-access-modifier-on-c-namespaces.aspxAs part of a Silverlight applicatin I am currently developing, I have a small API that ships with the application that allows extending it with more features. I had few "Default" implementations inside the API and hence I placed them within a NamespaceenCommunityServer 2.1 SP2 (Build: 61129.1)