Astrophysical jets are ubiquitous: this simple statement has become a commonplace over the last three decades and more as a result of observing campaigns using detectors sensitive from radio to gamma-ray energies. During this epoch, theoretical models of these sources have become more complex, moving from assumptions of isotropy that made analytic calculations possible, to fully anisotropic models of emission from the jets and their interactions with the interstellar and intra-cluster medium. Such calculations are only possible because we have extensive computational resources. In addition, the degree of international cooperation required for observing campaigns of these sorts is remarkable, since the instruments include among others the Ve...