In modern machine-tool practice, cutting temperatures are assuming increasing importance as cutting speeds and feeds are increased and new materials of construction are introduced. Although methods are available for determining experimentally the mean temperature on the tool face of a cutting tool, it is not possible to determine experimentally the influence of many of the variables influencing this temperature, or to measure conveniently its components. The analytical procedure to be followed in computing cutting temperatures is presented and illustrated by several examples. The relative importance of the several variables influencing tool-face temperatures is discussed and the variables of real significance are listed in order of importance. The only important thermal quantity of the system is the product of the thermal conductivity and the volume of specific heat of the workpiece. Analytical results are employed to explain the unusually high temperatures that are observed in machining titanium alloys.