This paper defines a language called Modula, which is intended primarily for programming dedicated computer systems, including process control systems on smaller machines. The language is largely based on Pascal, but in addition to conventional block structure it introduces a so-called module structure. A module is a set of procedures, data types and variables, where the programmer has precise control over the names that are imported from and exported to the environment. Modula includes general multiprocessing facilities, namely processes, interface modules and signals. It also allows the specification of facilities that represent a computer's specific peripheral devices. Those given in this paper pertain to the PDP-11.