Liquid cooled window assembly for an x-ray tube. In one example embodiment, an x-ray tube window assembly includes an x-ray tube window frame that defines an opening and an x-ray tube window configured to be attached to the x-ray tube window frame. When the x-ray tube window is attached to the x-ray tube window frame, the x-ray tube window substantially covers the opening defined by the x-ray tube window frame, and the x-ray tube window cooperates with the x-ray tube window frame to define a fluid passageway disposed about at least a portion of the opening. The fluid passageway includes an inlet and an outlet.