Аннотация:Ka-band VLBI capability now exists, is under development or is being considered at 22 sites around the world. Thus, there is now an opportunity to create a worldwide Ka-band VLBI network. This paper will examine the potential for a cooperative network capable of high resolution imaging and astrometry. Initial fringe tests on a few individual baselines have been successful and more tests are planned. With baselines approaching a Giga-lambda, a Ka-band network would be able to probe source structure at the nano-radian (200 μas) level and thus gain insight into astrophysics of the most compact regions of emission in active galactic nuclei.