Coefficients of friction obtained in metal cutting are often greatly different from those obtained with the same metal pair in conventional sliding-friction experiments. If only the rake angle is changed during cutting, a wide range of friction coefficients is obtained, and it is noted that the tendency toward complete adhesion of chip to tool increases as coefficient of friction decreases. These two apparent anomalies are explained by considering the fundamental mechanism of friction and the conditions which exist in cutting. It is shown that a coefficient of friction is inadequate to characterize the friction process in cutting, being mainly an indication of the normal stress on the tool face, and thus strongly dependent on the shear process in cutting.