Cloud Computing, Software as a Service (SaaS), Platform as a Service (PaaS), and Infrastructure as a Service (IaaS) are terms that denote new developments in the software industry that are completely changing the way software is produced, consumed, and distributed. In particular new PaaS business models have a disruptive effect on existing business models and require thorough business model innovation in the software industry. Despite their impact, PaaS business models have not been considered in a sufficient manner in literature yet. The paper at hand contributes to this gap by providing an overview of typical characteristics of PaaS based on a systematic literature review, a classification model of existing PaaS business models based on case studies and an overview of the current state and future development directions of PaaS.