Publisher Summary Microelectromechanical systems (MEMS) represent a highly multidisciplinary new technology with enormous commercial potential. Relying heavily on manufacturing methodologies originally developed by the integrated circuit (IC) industry, MEMS encompass themes of miniaturization, multiplicity of structures, and microelectronics. The enabling technology, commonly called solid-state micromachining, is an outgrowth of the IC process. Several MEMS devices are just beginning to show promise in such applications as automotive air bag deployment devices, rapid biochemical analysis systems, and projection displays. A variety of mechanisms involving mechanical, chemical, thermal, and radiant energy detection is developed for MEMS sensors and actuators. In this chapter, the use of piezoelectric materials for microsensor and microactuator applications is reviewed. Certain ferroelectric ceramics, particularly those with the perovskite structure, are known to have very high piezoelectric constants. The ferroelectric ceramics receiving the most widespread use as a bulk piezoelectric as well as a thin-film piezoelectric are in the lead–zirconate–titanate system. The discussion of the materials deposition of piezoelectric materials onto MEMS-based materials and the associated solid-state micromachining methods is also reviewed. The present work is based mainly on the use of the piezoelectric material lead–zirconate–itanate, or PZT, and its integration into MEMS sensors and actuators. The focus herein is to review recent progress in the use of piezoelectric thin films in MEMS-based sensors and actuators. In comparison to other physical sensing and actuation mechanisms, piezoelectric-based MEMS are generally attractive due to their high sensitivity and low electrical noise in sensing applications and high force output in actuation applications.