An effort to unify three major numerical methods in electromagnetics is presented. Harrington's direct method of moments, the iterative methods, and the reaction integral equation method are shown to be generally equivalent and are unified as the generalised method of moments. It is shown that the reaction integral equation method is in general a moment method, and that the moment method, when defined in a symmetric space, generally satisfies the reaction theorem, and therefore reciprocity. A broad, though limited, equivalence between the moment and the iterative methods is also demonstrated. A numerical example is discussed to illustrate these and other points.