A cam phaser is disclosed for adjusting the angular position of a camshaft relative to a crankshaft. In a first embodiment, a rotatable camshaft has an interior passageway and at least one cam operative to effect actuation of an engine valve. A first drive member is connectable to the crankshaft for rotational movement therewith. The first drive member is independently rotatably associated with the camshaft. A piston member is axially moveably disposed within the camshaft interior passageway and associated with the camshaft for rotation therewith. The piston member is further associated with the first drive member for rotation therewith and axial movement relative thereto. Axial movement of the piston member effects a change in the angular position of the first drive member. In a second embodiment, a rotatable tubular member has an interior passageway. A first drive member connectable to one or the other of a crankshaft or camshaft for rotational movement therewith is independently rotatably associated with the tubular member. A second drive member connectable to the other of a camshaft or crankshaft for rotational movement therewith is rotatably fixed relative to the tubular member. The first drive member is independently angularly positionable relative to the second drive member. A piston member is axially moveably disposed within the tubular member interior passageway and associated with the tubular member for rotation therewith. The piston member is further associated with the first drive member for rotation therewith and axial movement relative thereto. Axial movement of the piston member effects a change in the angular position of the first drive member relative to the second drive member.