The proliferation of Open Access (OA) business models has been rapid, presenting challenges for stakeholders in academic publishing in communicating and working effectively with one another. This article aims to clarify the myriad labels and terminologies used and address the inconsistencies and gaps in previous attempts to categorize OA models, ultimately supporting informed decision-making in the evolving landscape of academic publishing. It presents five core types, each with distinct characteristics and implications for funding, equity, and implementation: Operating at the level of individual pieces of content, transactional models expose authors to the financial implications of their decisions to make content open access; they often must pay out of their own grants or personal funds. (e.g. APCs) Driven by negotiations between libraries or consortia and publishers, bundle models typically operate at the level of the institution (or consortium). In many cases, authors are not exposed to the financial aspects of their decisions to make content open access. (e.g. Read and Publish) In cooperative models, the community acts in concert to spread the cost of open access as widely as possible. These models are typically initiated or driven by publishers. (e.g. Subscribe to Open for journals, Opening the Future for books) Sponsored models generally require a single actor to take responsibility for open access funding within a specific remit or title. (e.g. institutional support) Alternative OA models offer either immediate access to something other than the version of record (alternative OA: repository), or delayed access to the version of record (alternative OA: delayed).