Experimental results are presented that show relationships between grain structure and friction. In particular, grain boundaries cause changes in friction during single pass experiments using a diamond rip sliding on polycrystalline tungsten (polytungsten) and polycrystalline silicon (polysilicon). For polysilicon, the crystallographic orientation of individual grains is also shown to have n pronounced effect on friction. Since polysilicon is the major material used for microelectromechanical systems (MEMS), inter- and intragranular friction measurements are needed by scientists and engineers who hope to design and fabricate microminiature motors and other devicevs using polysilicon. For this reason, friction measurements were also made using an Atomic Force/Friction Force Microscope (AFM/FFM) which allows for measurements on a microscope.Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999