My research interests lie in high-energy astrophysics, particularly in the relativistic jets and very-high-energy particles created in extreme environments such as accreting black holes and supernova blast waves. I study these at all wavelengths from radio through to the highest-energy gamma rays. My research group works on both theory and experiment, with particular emphasis at present on the development of the next generation ground-based observatory for gamma-ray astronomy, the Cherenkov Telescope Array.