A formal method is introduced for the development and definition of command languages for heterogeneous computer networks. The network command languages are developed from the command languages of the systems constituting the network. This is done by defining a common presentation model for the system command languages and constructing the network command language by applying a composition principle to the commonly represented languages. The common presentation model is defined as a Vienna Development Method (Meta IV) abstract processor for command languages. System command languages are represented by means of predicate functions which are defined on the abstract domains of the abstract processor. This allows a straightforward formulation of the composition principle as a function for the logical combination of predicate functions. Two sample network command languages are composed out of two hypothetical command languages. The results are related to the International Organization for Standardization Open Systems Interconnection model (ISO OSI).