Many library directors and Associate University Librarians (AUL) are looking for support in diversifying library collections. Ithaka S+R developed this guide to contribute to the efforts emerging in response to this need. The guide presents a series of takeaways, exercises, and examples that those in leadership positions in academic libraries, including deans, directors, and collection heads, can utilize to begin, supplement, and review their library's efforts to diversify collections. The guide is grounded in and advances the following foundational principles: (1) Libraries have a unique role in supporting institution-wide DEI goals through their collection strategies; (2) Meaningful contributions to collections work can come from library staff at all levels; therefore a library-wide strategy for diversifying collections must foster shared values. New organizational directions that involve cultural, budgetary, and policy change must have strong support from directors and collection managers as primary facilitators of large-scale change; and (3) Diversifying collections may require senior leadership to take risks in the face of opposition or inaction internally and externally The guide is designed to help library leadership take action in ways that are grounded in the reality that every institution is unique. There is no "one size fits all" approach to address any of the field's key issues, and the guide therefore provides a framework rather than a prescriptive method for universal application. [This project was supported by EBSCO.]