Charges in gauge theories

In this article we investigate charged particles in gauge theories. After r eviewing the physical and theoretical problems, a method to construct charg ed particles is presented. Explicit solutions are found in the abelian theo ry and a physical interpretation is given. These solutions and our interpre tation of these variables as the true degrees of freedom for charged partic les, are then tested in the perturbative domain and are demonstrated to yie ld infra-red finite, on-shell Green's functions at all orders of perturbati on theory. The extension to collinear divergences is studied and it is show n that this method applies to the case of massless charged particles: The a pplication of these constructions to the charged sectors of the standard mo del is reviewed and we conclude with a discussion of the successes achieved so far in this programme and a list of open questions.