Plastics are an integral material to the European economy, but they remain embedded in a system that produces waste by design. The circular plastics economy has been envisioned as an alternative that will preserve the value of plastics while also reducing their negative impacts. In the transition towards such a system, the development of innovative circular business models (CBMs) plays a vital role. CBMs in the circular plastics economy remain highly centered around recycling, a widespread strategy that does not require a shift in the core business model. While undoubtedly beneficial, incremental progress is not enough to enact a circular transition. Thus, this paper explores the business models of circular start-ups (CSUs) as they are expected to adopt more disruptive CBM approaches that might accelerate the circular plastics transition. The method combines a literature review and multiple case study. Research-based CBM design principles are derived from a systematic review of the literature on CBMs and their barriers/drivers. These are then validated through semistructured interviews of Dutch start-ups in the circular plastics economy, while simultaneously revealing new insights from practice. The synthesis of both academic and practitioner knowledge results in robust recommendations for future entrepreneurs in designing circularity into their business models. Upon completion, the study will have mapped CBMs in the Dutch circular plastics economy, created a deeper understanding of barriers and drivers influencing CBM in this context, and distilled a set of recommendations for entities in the plastics economy aiming to design new circular business models.