Cutting tool wear is a production management problem for manufacturing industries. It occurs along the cutting edge and on adjacent surfaces. This article describes steady-state wear mechanisms, tertiary wear mechanisms, and tool replacement. It provides information on tool failure and its consequences. The article details the modeling of tool wear by using the Taylor's tool life equation. The article concludes with information on the requirements of a successful tool life testing program: the test plan objective, designing the test, conducting the test, analyzing the results, and applying the results.