Documentation of local policies, workflows, and procedures is an important activity for cataloging and metadata units. But creating and maintaining documentation is a huge task that is not always a high priority. Librarians at the University of Minnesota Libraries planned a documentation hackathon, CatDoc HackDoc, with three primary goals: to update a large amount of documentation quickly, to apply accessibility best practices to all documentation, and to bring new staff into the documentation workflow. This article describes the event's planning process, structure, and outcomes, and offers guidance on how others can adapt the CatDoc HackDoc model in their own organizations. transitions, both by increasing staff confidence and improving process efficiency. When good documentation is in place, new staff members should not have to "reverse engineer" procedural steps or invent (and document) an entirely new procedure where a previously undocumented one had been in place.Another critical function of documentation is to encourage consistency of practice. This is especially true when more than one staff member is responsible for the same or similar cataloging and metadata tasks. Staff who began working for the library at different times may have learned their jobs under different standards and practices or may have learned their jobs under different supervisors or lead workers. As job responsibilities, metadata standards, and library systems all change over time, it is challenging to keep everyone "on the same page." Ongoing attention paid to documentation can help alleviate this problem. 1 Accurate, up-to-date documentation is also a valuable tool for data analysis. Five decades after the invention of MARC, and 30-40 years after many libraries implemented their first integrated library system, the need for documentation showing how library data practices have changed over time is acute and growing. Thoughtfully maintained documentation can explain puzzling elements in legacy data, help identify areas for data remediation, and serve as an informal registry or key for analysis projects drawing on library metadata. Whatever the rationale for prioritizing documentation, it is important to think of documentation as an ongoing process, rather than as a project with a clearly defined endpoint. Good documentation has a lifecycle. The components of the documentation lifecycle may vary slightly, but a simple lifecycle might include drafting, publishing,