The S-Matrix in the Heisenberg Representation

A method is described whereby the S-matrix can be formulated directly in the Heisenberg representation. This has the advantage over the customary formulation in the interaction representation in that the concepts of space-like surfaces and their normals need never be introduced. Quantum electrodynamics and the $\beta$ formalism of charged mesons are treated as illustrative examples; in particular, it is shown that general rules for writing down the elements of the S-matrix for the latter case may be immediately inferred.