Designing a cellular manufacturing (CM) system involves three major decisions: cell formation (CF), cellular layout (CL), and cellular scheduling (CS). The integrated design of CM systems is investigated in this paper by proposing two mathematical models. The first model integrates cellular layout problem with cell formation problem to determine optimal cell configuration and the layout of machines and cells in order to minimize the total movement costs. The second model takes also the cellular scheduling into consideration with the objective of minimizing the total completion time of parts. Two genetic algorithms are developed to solve the real-sized problems. The proposed models are formulated as mixed integer linear programming, and two numerical examples are solved in order to investigate the effects of integration in the CM systems design. The results show that considering CF, CL, and CS decisions in a simultaneous manner can significantly improve the performance of the CM systems.