China's BeiDou navigation system (BDS) has evolved from the demonstration navigation satellite system (BDS-1) to the regional navigation satellite system (BDS-2). Now, the global BeiDou navigation system (BDS-3) is in construction and is proceeding well. The design and functions of BDS-3 are quite different from those of both BDS-1 and BDS-2. In this paper, the general design, the coordinate reference system, and the system time basis of BDS-3 are introduced. Several new payloads designed to accomplish different objectives are described as well as the platforms on which they are hosted. Since BDS-3 consists of several different constellations, the general service capabilities and special service functions provided by these different constellations are described. The performances of the initial BDS-3 platforms are evaluated based on the available eight-medium Earth orbit (MEO) satellite configuration. The results of satellite orbit determination and prediction with and without the BDS-3 inter-satellite links (ISL) are compared and analyzed.