This document summarizes the different types of open access publishers and their business models. It identifies several types of publishers, including large and small professional organizations, university libraries and presses, and scholar publishers. The business models discussed include article processing charges, volunteer efforts, and other sources of funding like grants, subscriptions, and advertising. Open access publishing varies by field, with biomedicine dominating, while engineering, social sciences, and humanities have fewer open access options. Different types of publishers tend to focus on different subject areas within open access.