A frequently advanced claim in contemporary science policy is that interdisciplinarity is especially well suited for being ‘transformative’ and for bringing about ‘major breakthroughs’. Thus, it is expected that, in contemporary science, major progress will come primarily from interdisciplinary research (IDR). Often in this dis-course, interdisciplinarity is also expected to integrate the involved disciplines or specialties. This chapter will provide a philosophical qualification of this political discourse by examining how interdisciplinary progress can be characterised. I shall argue that in addition to the categories of incremental and transformative progress that are well known from mono-disciplinary science, IDR can sometimes also offer another category of progress that I shall call quasi-transformative. In examining these three kinds of interdisciplinary progresses I shall argue, first, that interdisciplinary progress does not necessarily require a specific type of integration between the involved disciplines or specialties, second, that social relations between scientists with different areas of expertise may play a crucial role in especially transformative progress, and third, that different disciplinary perspectives on what constitutes progress can draw wedges between scientists from different disciplines.