This study focuses on theory building providing a holistic conceptual framework that consists of an ontology based OSS business model and an OSS business model taxonomy. The study extends existing theory in OSS business models and corresponding taxonomies, based on the structured-case methodological approach. An exploratory study is conducted in two research cycles, for the identification, validation, and evaluation of the critical constructs of an OSS business model. Results reveal that OSS business models differ from traditional software business models, having specific features that affect the software value chain, the infrastructure, and the revenue model of an OSS oriented firm.