The base type is the type from which the current type directly inherits. Object is the only type that does not have a base type, therefore Nothing is returned as the base type of Object.
Interfaces inherit from zero or more base interfaces; therefore, this property returns Nothing if the Type object represents an interface. The base interfaces can be determined with GetInterfaces or FindInterfaces.
If the current Type represents a constructed generic type, the base type reflects the generic arguments. For example, consider the following declarations:
Class B(Of U)
EndClassClass C(Of T)
Inherits B(Of T)
For the constructed type C<int> (C(Of Integer) in Visual Basic), the BaseType property returns B<int>.
If the current Type represents a type parameter of a generic type definition, BaseType returns the class constraint, that is, the class the type parameter must inherit. If there is no class constraint, BaseType returns System.Object.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2