There are several sources that indicate a remarkable increase in the adoption of open source software (OSS) into the technology infrastructure of organizations. In fact, the number of medium to large organizations without some OSS installations, is surprisingly low. This move to open source (OS), as well as the obvious advantages thereof, have motivated the CSIR of South Africa to investigate the adoption of OSS across the institution for all aspects of its operations. In launching this endeavor, it became apparent that there are very limited resources available, locally or internationally, that documented process related information about organizational OS migrations. This lack of information provides the motivation for this research that investigates the use of process reference models to capture the process related information for an organization wide migration from proprietary software to OSS. In order to develop the necessary process reference models, the specific process models for the CSIR OS migration were captured, and, using a repeatable method based on reference model criteria, the generic process reference models for an organizational OS migration were extracted and documented. It is our firm belief that these process reference models would provide a baseline for the processes needed when any organization considers open source adoption or organization-wide OS migration.