This document compares the planning, collections, facilities, staffing, partnerships, priorities, and challenges of four 21st century medical libraries established between 2000-2009: 1. The Commonwealth Medical College Library (2009) focused on electronic collections, will occupy a new facility in 2011, and aims to support a community-based medical school across regional campuses. 2. The University of Hawaii at Manoa Medical Library (2005) has over 90% of its collection online, partners with other libraries, and supports a community-focused medical school. 3. The University of Arizona Phoenix Medical Library (2007) has a highly curriculum-focused digital collection and partnerships across universities to serve its medical and pharmacy programs.