This paper reviews some of the major concepts involved in the design of a microprogrammed control for a general purpose data processor. The areas discussed are timing, control store cycle design, bit dimension design and word dimension design. The design considerations are presented from the perspective of a system design engineer concerned with producing a viable product design. Although the concepts are presented in the context of a medium to large scale processor design; they are, for the most part, applicable to the design of any microprogrammed system.