Abstract: Gear transmission is, at the present time, the most widely used type of transmission in both the machine tools, and the general machinery industry, and for this reason, the cutting of gears may play an important role in national economics. The hobbing of gears constitutes one of the most important ways of processing, as it forms The principal method for cutting gears before beat treatment, and is also the final process for gears that do not under-go heat treatment. The cutting of gear teeth shapes is the most difficult and the most complicated procedure in the gear processing technology, and it is the purpose of this paper to try to give a detailed analysis of the precision of gear hobbing in order to determine methods for its improvement. This paper presents the discussion mainly from the following two points of view tools and machinery, as these two factors form the basic sources of error in gear teeth shapes.