The initiating step in cutting-tool wear is postulated as a temperature-dependent migration of chip metal into the tool. The migrated metal softens the tool, which allows wear particles to adhere to the moving chip and be carried away. The kinetics of these processes are developed quantitatively to yield an expression which explains the Taylor equation in terms of the fundamental parameters of cutting. The action of cutting-oils is regarded as a competition between the rate of alloying and softening of the tool by migrated chip metal and the rate of reaction of the migrated chip metal with the cutting-oil additive. The kinetics of these competing processes are then developed quantitatively to explain the behavior of the Taylor equation when metal is cut in the presence of cutting-oil.Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Toronto, Canada, October, 1957.