Considering GLONASS as one of the pillars of the international Global Navigation Satellite System (GNSS), the Russian Federation works toward the integration of GLONASS with other navigation systems, cooperates with the internal user community, and contributes to the development and coordination of standards concerning GLONASS and the combined use of GLONASS and the global positioning system (GPS). This work is pursued in conformity with recommendations of respective international organizations. Most users recognize that the GLONASS/GPS combination has better characteristics in terms of availability, accuracy, integrity, and so on. However, the combined use of these satellite systems raises problems that must be addressed. This article reviews problems encountered when using two different navigation systems. Solutions developed thus far are outlined. The potential of GLONASS and approaches for high accuracy UTC time transfer are discussed. The transformation between the WGS 84 and PZ 90 reference frames and their conformity with the international terrestrial reference frame (ITRF) is considered. Various solutions are viewed in connections with recommendations made by the International Civil Aviation Organization (ICAO), the Global Navigation Satellite System Panel (GNSP), and the Consultative Committee for Definition of the Second (CCDS) concerning the desirability of using either or both systems interchangeably. © 1999 John Wiley & Sons, Inc.