The Hartebeesthoek Radio Astronomy Observatory has played a key role in the development of very long baseline interferometry (VLBI) in the southern hemisphere since 1971. This paper describes how the VLBI programme evolved and the instrumentation used. Contributions to high resolution mapping of compact radio sources are described, for both the Southern Hemisphere VLBI Experiment, SHEVE, and for Global networks, where HartRAO has made significant improvements in the N-S resolution. The unique geographical location of the telescope has been used to establish the terrestrial reference frame in the southern hemisphere and to measure tectonic motions over the past nine years. The Observatory has also been a fundamental station in extending the celestial reference frame defined by extragalactic radio sources to the southern hemisphere, and results of these programmes are given.