Precise geodesy with the Global Positioning System (GPS) emerged in the early 1990s from a decade-long incubation to find vigorous application worldwide. Today we enjoy a full 24-satellite constellation, a new generation of high-precision receivers at about one-third the 1991 cost, a growing permanent global network, and a vital International GPS Service to support GPS geodesy worldwide. In addition, dedicated regional GPS networks are springing up on every continent. The period has been marked less by conceptual advance than by disciplined application and refinement. Here we review the key developments in receivers and networks, and in understanding the environmental factors that limit GPS geodetic performance.