Twenty years ago, when I presented my thesis on “The position of members of resistance movements under international law” at a public graduation ceremony in the Amsterdam University auditorium, Professor Tammes was my Promotor. For many years he had watched with interest over the progress of the thesis and had helped me, in our frequent exchanges of views, to deal with the difficulties and uncertainties of this part of international law. Bearing in mind the resistance movements of World War II, the subject seemed to be of more than merely theoretical importance, though it did offer important theoretical aspects, as will appear from the following pages.