The essential part of the theory of Enterprise Process Control (the EPC theory) is a formal description of the framework EPC system. It is a universal reference model of integrated management and process control systems for all enterprises, regardless of their trade and size. Basic notions of the EPC theory have been presented in the paper. Certain definitions of broadly known terms (e.g. organizational system, process, resource, control unit, functional layer) are slightly different than the ones that are most often formulated. The purpose of these modifications is precise presentation of relationships between defined notions. Furthermore many new notions (functional subsystem, functional unit, transition unit, information place, reengineering layer, readiness variant, organizational resources and the like) have been introduced. They are necessary for presenting organizational and functional structure of the framework EPC system. The EPC theory has deductive nature and its notions are formulated on the basis of the more general, previously defined ones.