In the conditions of formation of documentation systems of Ukraine, being integrated into world similar systems, the development of branch documentary mechanisms, their integration among themselves at the national and international level becomes relevant. Of particular importance among such mechanisms is the system of legal documentation and its subordinated communication system of documentation of the legal sphere. The question of formulating the concept for the latter and clarifying its relationship with other known documentation systems is in demand. Current legislation, available scientific and lexicographical works do not provide an unambiguous answer to this question. Therefore, there is the necessity of: specialized study and generalization of all sources related to this issue; critical rethinking of the provisions developed by practitioners and scholars in this field; making of an unambiguous position on correlation of terms of communication system of documentation support of legal sphere, disciplinary, basic and infrastructural systems of documentation. Arguments in favor of distinguishing these documentary phenomena and their relationship, taking into account vertical (hierarchical) and horizontal connections, were formulated. The results of the study made it possible to: develop an author's definition of the communication system of documentation support of the legal sphere; to determine the regularity of its subordination to the following systems: the system of legal documentation -the public disciplinary (branch) system of documentation -the general system of documentation; to prove its formation as a result of a combination of practical, educational and scientific "basic" areas of law, as well as functional (infrastructural) documentation systems, which are diffuse in nature: regulatory, managerial and organizational-administrative.