A general approach to an interpretation of the existing terminology and to an application of the service robot component modularity classifications is considered. Classifications of modules according to functional and structural criteria are presented. Classification of modules according to functional criterion was developed for machine-building products and it is of little use for robot structure descri ption. Structural classification is oriented on a modular presentation of various robot subsystems but it is rather hard to use it to describe modular mechanical structures. Concepts of the modular robot architecture development are considered from positions of the component and functional approaches. The component approach is based on the Design Structure Matrix that gives a possibility to optimize the modular robot structure according to an objective function. The functional approach is used to analyze a composition of the robot functions and to decompose functions onto sub-functions to determine a modular composition of the robot. A brief overview of the morphotronic methods being developed currently and the contact & channel method used for the robots structural design is presented. Morphotronics is a new approach to the formal synthesis of the generalized system architecture. The contact & channel method enables to represent mechatronic robotic devices as a composition of components with inputs and outputs and to develop modular structures.