Microelectromechanical systems are ideal tools for conducting fatigue experiments on small structures. When integrated with electron microscopy techniques, microelectromechanical testing systems provide unique platforms for investigating micromechanisms of fatigue crack propagation along interfacial thin films. We present two examples from our recent work where piezoelectrically actuated microelectromechanical systems were built to examine fatigue crack growth along interfacial thin films. The first example investigates fatigue cracking of the grain boundary film in a polycrystalline ferroelectric ceramic where field-induced cavitation and ligament bridging played a significant role. The second example examines fatigue crack growth in a metallic thin film confined by the rigid substrates, where the stress-induced voiding of the thin film was the dominant fatigue crack growth mechanism. Mechanics of piezoelectric driving force for the crack growth in the microelectromechanical systems will be given and analyses of the pertinent crack growth mechanisms will be discussed.