A metal or alloy must be tuned to the desired properties before use in several engineering applications. Most of these properties depend upon the structure, and suitable heat treatment processes can produce the preferred phases. In a typical heat treatment process of steel, it is first heated to some temperature to form austenite, held at that temperature for the required time, and then finally cooled down to room temperature. The transformed products from austenite determine the physical and mechanical properties of the steel. Therefore, looking at the importance of a detailed understanding of the heat treatment process, this chapter mainly focuses on different heat treatment practices that are commonly used for steels since steel is the most essential and versatile engineering alloy.