The "mechanical" part of "microelectromechanical systems" (MEMS) requires knowledge of mechanical properties to predict relations between forces and displacements. Young’s modulus and Poisson’s ratio are needed for elastic response, and the strength of the material is needed to determine the allowable forces or displacements. Tensile testing is the preferred approach for structural materials because its uniform stress and strain fields enable direct determination of mechanical properties according to their definitions. Tensile testing of small thin-film specimens presents three challenges - preparation and handling of the specimen, measurement of small forces, and measurement of strain in the specimen. The author and colleagues at Hopkins have developed techniques and procedures for tensile testing of polysilicon, silicon nitride and silicon carbide. It is easier to measure mechanical properties of MEMS materials indirectly by modeling microdevices and extracting properties. One can fabricate a comb-driven resonant structure and use the measured resonant frequency to determine the modulus. Thin membranes of different shapes can be pressurized, and the measured displacements used to determine both Young’s modulus and Poisson’s ratio. Cantilever or fixed-end beams can be deflected electrostatically to measure modulus. However, none of these indirect approaches permit measurement of all the three properties (modulus, ratio, strength) simultaneously as does the tensile test. This presentation summarizes the current state-of-the-art in terms of test methods and the values of the polysilicon and other materials used in MEMS.