The core WPF assemblies are,
WindowsBase.dll:- It defines the core types constituting the infrastructure of WPF API.
PresentationCore.dll:- Defines numerous types constituting foundation of WPF GUI layer.
PresentationFoundation.dll:- It defines WPF control types, animation & multimedia support, data binding suport and other WPF services.
Besides these three libraries WPF also uses an unmanaged binary called milcore.dll which acts as a bridge between WPF assemblies and DirectX runtime layer.