How can I document a namespace?

A namespace can be documented as any other code construct - directly in the source code. Just select any file that contains the namespace declaration and add an XML comment above the namespace/Namespace keyword. You can use VSdocman's Add XML comment option from the context menu or the comment editor.

C#:

/// <summary>This is my namespace.</summary>
namespace SampleClassLibrary
{
...
}

VB .NET:

''' <summary>This is my namespace.</summary>
Namespace SampleClassLibrary
...
End Namespace

Visual Studio will show a warning that an XML comment is not allowed on a namespace. You can whether ignore the warning or you can suppress it.

A single namespace can be used in multiple files, but you only document it in a one. It doesn't matter which one it is. If you add an XML comment for the same namespace on multiple places, VSdocman will show a warning during the compilation and a comment from a random place will be used.

In VB .NET, the root namespace has no source code representation. See how to document VB .NET root namespace.