Various kinds of ‘failures’ are a constant companion of scientific work, as research frequently does not produce the results that were expected or hoped for. In this talk, I will address the tricky role of failures, understood as disappointed expectations concerning the outcomes of research processes, in scientific knowledge production. In particular, I will address an apparent tension between theory and practice that is expressed in valuations of failure as integral and crucial element in scientific progress, on the one hand, and an apparent lack of communication about failure in scientific communities, on the other hand. This tension will be illustrated with classical arguments from the literature of the history, philosophy and sociology of science and with observations from a recent empirical project on failure in science. Thus, the talk wants to invite critical reflection on a ubiquitous but neglected part of research.