K ->pi pi phenomenology in the presence of electromagnetism

We describe the influence of electromagnetism on the phenomenology of K --> pi pi decays. This is required because the present data were analyzed with out inclusion of electromagnetic radiative corrections, and hence contain s everal ambiguities and uncertainties which we describe in detail. Our prese ntation includes a full description of the infrared effects needed for a ne w experimental analysis. It also describes the general treatment of final s tate interaction phases, needed because Watson's theorem is no longer valid in the presence of electromagnetism. The phase of the isospin-two amplitud e A(2) may be modified by 50 --> 100%. We provide a tentative analysis usin g present data in order to illustrate the sensitivity to electromagnetic ef fects, and also discuss how the standard treatment of epsilon'/epsilon is m odified.