This chapter discusses processes of linguistic convergence in medieval Romance: the development of supra-regional spoken varieties and the emergence of supra-individual orthographic conventions. It reserves the terms koiné for spoken supra-regional varieties and koineization for their emergence, whilst recognizing their mutual relationship with convergence processes in the written scriptae. The chapter outlines diachronic areas of convergence or divergence, as certain processes taking place in these areas are to be the focus of attention. It considers the development of koineization tendencies and writing traditions in medieval Romance languages as a whole, and observes certain parallels between the different areas, which enable a classification into different phases to be made. However, these parallels take on quite different shapes in the individual areas. The chapter also presents some remarks on Romance language areas to survey some general aspects, highlighting some of the crucial issues and providing basic bibliographical information.