Generalizations of the virial theorem are derived: In atomic physics, in systems including electromagnetic radiation, in Newtonian gravitation, and in general relativity and also some types of nuclear forces. The cases discussed are limited to potentials which can be produced by the exchange of one particle, which include potentials of the form1/r. The method used is to set equal a change in energy produced by an infinitesimal similarity transformation to a change of energy obtained by a first-order perturbation.