French conventionalism originated at the turn of the 19th century. The views of Duhem, Poincaré and Le Roy are usually ranked under this heading and they will be presented in some detail in what follows. The purpose of this paper is to show the significance and considerable influence of French conventionalism on the development of philosophy and to present, in particular, its repercussions in Polish philosophy. There is a number of different types of confusions and misinterpretations surrounding conventionalism as a whole. It is sometimes seen as a peculiar and rather insignificant episode in the history of philosophy of science. Its crucial role and marked impact on various philosophical ideas is sometimes ignored, especially its contribution to the anti-inductionistic and anti-positivistic turn.