We present a number of concepts and hypotheses concerning the impact of the political opportunity structure on the mobilisation pattern of new social movements in Western Europe. The hypotheses refer to the general level of mobilisation in a given country, the general forms and strategies of action employed, the system level at which mobilisation is typically oriented and the development of the level of mobilisation across time. The hypotheses are tested in a comparative analysis of France, Germany, the Netherlands and Switzerland. The analysis reveals country-specific variations in the mobilisation patterns of new social movements, which are largely in line with the theoretical expectations and serve to confirm the relevance of the political process approach for the study of social movements.