Most of tool wear studies are classified as empirical (e.g. Taylor’s equation); thus, they do not bring out the physical nature of the wear phenomenon. Consequently, tool life in general cannot be predicted by extending the result from one study. By understanding the physics behind the process, the important wear mechanisms can be identified. By constructing a wear model for each wear mechanism with more fundamental quantities such as materials properties, these models can be combined and extended to estimate tool life. This should be the ultimate goal of tool wear research in machining. However, a major gap exists between the current understandings of tool wear and the ultimate goal of tool wear research. This paper will describe how cutting tools are being worn down during machining based on the physics behind tool wear. © 2007 Inderscience Enterprises Ltd.