After a brief review of the challenges of calculating scattering amplitudes for electric and magnetic charges, as well as a discussion of Wigner's ``little group'' and the helicity amplitude approach, I will discuss how S-matrix calculations can be extended to include magnetic charges. The answer involves an extension of the concept of helicity to a ``pairwise helicity'' involving two particles. \\ \\ The seminar is only on zoom: https://ijclab.zoom.us/j/94900481972 \\ \\ https://indico.in2p3.fr/category/870/