The fact that temperature can affect the performance of friction material has long been recognized, and many studies of the phenomena have been made. For the most part, results have been contradictory and indicate a complex relationship between temperature and other variables that constitute the conditions of use. This paper offers a report on the continuing effort to establish the extent of change produced and the mechanism by which such change is effected. Data are presented on SAE #2 machine test of three friction materials in three oils controlled at varying temperature level.How the temperature effects can be further modified by pressure or power loadings are also demonstrated. In addition, study of friction hysteresis with temperature-performance at temperature as affected by previous history - is included. Theories are proposed to explain trends noted in the data. While these are intended to aid in optimizing design for specific units, the need for further study to improve understanding in this area is implied.