Context: Open source software (OSS) is changing the way organizations develop, acquire, use, and commercialize software. Objective: This paper seeks to identify how organizations adopt OSS, classify the literature according to these ways of adopting OSS, and with a focus on software development evaluate the research on adoption of OSS in organizations. Method: Based on the systematic literature review method we reviewed publications from 24 journals and seven conference and workshop proceedings, published between 1998 and 2008. From a population of 24289 papers, we identified 112 papers which provide empirical evidence on how organizations actually adopt OSS. Results: We show that adopting OSS involves more than simply using OSS products. We moreover provide a classification framework consisting of six distinctly different ways in which organizations adopt OSS. This framework is used to illustrate some of the opportunities and challenges organizations meet when approaching OSS, to show that OSS can be adopted successfully in different ways, and to organize and review existing research. We find that this research does not sufficiently describe the context of the organizations studied. It is furthermore fragmented and fails to benefit fully from related research fields. Finally, we present directions for future research.