Purpose – This paper aims to review research on outsourcing of knowledge processes to establish the current body of knowledge and, on this basis, to identify gaps in our understanding. This action will justify further research activities and clarify where no future research is currently needed. Design/methodology/approach – The study consists of a systematic review of 24 refereed empirical articles on outsourcing of knowledge processes. Findings – Five themes were identified: outsourcing of knowledge processes, outsourcing and collaborative agreements between knowledge-based firms, factors affecting successful knowledge outsourcing, knowledge management and knowledge outsourcing and other outsourcing issues. There seems to be a lack of understanding concerning knowledge process outsourcing. Research limitations/implications – This study may not have enabled a complete coverage of all empirical articles in the field of knowledge process outsourcing. Yet, it seems reasonable to assume that the review process covered a large share of studies available. Originality/value – To the best of the authors’ knowledge, no systematic literature review on this topic has previously been published in academic journals.