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This symposium comes at an interesting time in the history of Very High Energy (VHE) gamma-ray astronomy. The TeV source catalog has now swelled to respectable proportions and is attracting increasing attention amongst theorists and observers at longer wavelengths. The atmospheric Cherenkov imaging technique has been demonstrated to be an effective tool at energies greater than 300 GeV. No other technique has been suggested that is competitive in the energy region from 50 GeV to 50 TeV; clearly, further efforts to improve and extend the technique are justified. In fact a new generation of instruments is under development and the next symposium will surely be dominated by their achievements.

It is 4.5 years since the first symposium on the TeV Astrophysics of Extragalactic Sources was held at the CfA in Cambridge (1). These proceedings show that there has been significant progress since that time. As we discuss below, not only has the number of detected objects increased (and with this the depth of the universe that is probed) but the number of kinds of extragalactic sources has also increased; this is a prediction of good things to come as the sensitivity and range of the telescopes is improved.

Although there has been considerable activity on the theoretical front with the development of models to explain the observed phenomena, there is still no consensus even on such basic things as the nature of the progenitor particles. This is still an observation-driven field and seems likely to be so for some time to come. Clearly the results of multi-wavelength observations are indicative of complex mechanisms and the simple models that have been proposed have a long way to go in providing a full explanation.

Here we will not attempt to give either a summary of the symposium or a comprehensive review of the field. The papers in this volume speak for themselves and describe the progress in the field; recent reviews can be found elsewhere (2); (3); (4); (5). The next generation of instruments: CANGAROO-III, HESS, MAGIC and VERITAS will reach a level of sensitivity such that they are effectively limited by the cosmic electron background; they should all be online by 2004-2006.

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