This presentation will focus on the electro-mechanical properties of single crystals of relaxor ferroelectric PZN–PT. The characterization work begins with measurement of the drive capability of the material as a function of preload. These measurements were made by loading specimens at constant stress levels and then cycling the electric field while monitoring the resulting strain. Results to be presented are curves for stress/strain at various electric field levels, and strain/electric field and electric displacement/electric field at various constant stress loads. A second set of experiments was performed by placing the specimens in bending. In this arrangement, the tensile and compressive stress/strain behavior are determined simultaneously. This clearly shows the effects of material nonlinearity. The final set of tests takes a close look at fatigue of the material. Small cracks are intentionally placed in specimens and then the electric field is cycled. Observation of fatigue behavior will be discussed.