Abstract: The study deals with the conceptual basis of the calculus of functional objects as a formal theory of systems. The basic concepts and definitions of the calculus of functional objects are presented within their framework the functional object is considered as a system described in terms of the system-object approach "unit-function-object". Formal bases for describing the methods of nodal objects within the framework of the supposed calculus are considered, basic constructions of the language for describing functional nodes are proposed.