Free and open source software development (FOSS) used to be associated with an ideologically driven movement built around communities of voluntary members, organizing resistance against proprietary software development. Today, however, software firms perceive FOSS as a source of innovation. Previous research has investigated what this change has meant to movement driven FOSS, but we still need more knowledge about the professional programmers and their way of organize business driven open source software development in their daily practice. This article investigates the interpretative guidelines or justifying arrangement that guide their use of FOSS. The analysis is based on 30 interviews that were done during 2008-2009 with programmers who were employed either by software firms that had come to a point where they started to adopt open source, or by firms that always based their business on open source software development. Theoretical concepts that were used in the analysis mainly derive from the economic sociology of Luc Boltanski and Laurent Thevénot, and the results indicate the emergence of a new spirit of business driven open source, consisting of a combination of different justificatory logics. This new spirit is described as an arrangement guiding how professional programmers in today’s software industry perceive the worth of using open source code in their developmental work.