The present study aims to examine the cooperation related to the development of international copyright law from the perspective of the Magyar Színpadi Szerzők Egyesülete (MSSE, Hungarian Playwrights’ Association). The association, founded in 1904, played an outstanding role in dealing with the shortcomings of Hungarian copyright law and the protection of the moral and financial interests of Hungarian playwrights/stage authors. Thus, the purpose of this paper is to present the Association’s contribution to various milestones of the international copyright field, such as the Berne Convention for the Protection of Literary and Artistic Works and the founding of the International Confederation of Societies of Authors and Composers (CISAC). The annual conferences of the world organization, especially the 1930 Budapest International Congress of Authors, an important event of Hungarian cultural diplomacy, shall also be presented in the study. Further aims of the study include shedding light on how national and international copyright cooperation developed in the first half of the 20th century.