A technique in radio interferometry where telescopes, often many thousands of kilometres apart, may be operated as an interferometer to achieve angular resolutions better than 0″.001. Each telescope works independently, recording the signals together with timing information on arrays of hard disks. Later the data are replayed and the signals combined. In the new technique of e-VLBI, the data are transferred in real time to the central processor over the Internet. A side-benefit of VLBI work is the location of the observatories to accuracies of a few centimetres, useful in the study of continental drift. Examples of VLBI arrays are the European VLBI Network (EVN), the Very Long Baseline Array, and the Australia Telescope. The advent of space-borne radio telescopes such as RadioAstron is extending VLBI baselines to hundreds of thousands of kilometres.