Numerical evidence is everywhere and how best to handle and leverage it is a growing concern in the academic world in general and the academic library world in particular. Libraries are not only storehouses and key contacts for library patrons in accessing numbers, but are also collectors and users of their own data, which is integral to the functioning of the library itself. The essays in Library Data: Empowering Practice and Persuasion focus on interpreting and using library-generated and outside data in support of data-driven practice and data-strengthened persuasion. The collection includes such topics as how to make data presentations appealing and effective; applying capital-budgeting models to libraries; and using data for evaluation and improvement of collections and services. Articles also cover specialized scenarios, including reference, collection development, serial acquisitions, institutional repositories, web site design, interlibrary loan, and bibliographic instruction.