The paper summarizes the present status of development of Computer Integrated Manufacturing (CIM) and outlines the difficulties and obstacles in the practical realization of CIM. The paper starts from an analysis of the main subsystems constituting CIM: Computer Aided Design (CAD), Computer Aided Manufacturing (CAM), and Management Information Systems (MIS). The meaning of integration within these subsystems is clarified and difficulties observed here are pointed out. Some major research and development efforts undertaken presently in the U.S. are briefly discussed. The paper describes the main problems which occur in the attempts to integrate between subsystems. The key role of CAD as the source of all CIM data flows is discussed; and the role of the numerical control technique in providing means of subsystem integration is evaluated. Difficulties occuring in particular at the CAD-CAM interface are discussed. The paper ends with conclusions regarding several possible research directions to accomplish the creation of real-life CIM systems.