Machinability is a feature of the material being processed and can only be changed by changing the properties of the material. This is achieved by changes in the chemical and physical properties of the material. The aim of this compilation study is to explain the machinability concept extensively and to discuss the works done to improve the machinability of the steels. When evaluating the machinability of steels, their mechanical properties and especially their hardness are taken into consideration. The machinability depending on the microstructures formed by heat treatments and the amount of carbon which is the main element that increases the hardness are evaluated. However, the addition of S, Pb, Bi and Te etc. elements increase the machinability without significant changes in the mechanical properties of steel. The machinability is graded by taking into consideration of the cutting force, tool life, surface quality and chip shape generated during the machining process. The effect of chemical composition and microstructure on machinability of steels is one of the most investigated subjects in the field of materials and metallurgical science. In addition to the variables in the production process of steel, microstructure-based machinability assessments generated by heat treatments are also important. The heterogeneous distribution of the phases in the microstructure provided by the mentioned processes should not be ignored in the machinability assessments.