More than fourteen years have passed since the second edition of the Map and Geography Round Table's Guide to U.S. Map Resources appeared in 1990. The third edition offers users a detailed snapshot of and guide to hundreds of map collections and cartographic resources in libraries and repositories throughout the nation. Substantial changes have occurred within library map collections over the past decade and a half, and not surprisingly, the computer has been at the core of most of these innovations. Geographic information systems (GIS), the World Wide Web, email, Portable Document Format, data sets, the Internet and digitization have all played revolutionary roles in transforming libraries--and map collections in particular--over the past fifteen years. Today's librarian who works with maps is no longer limited by the contents of his or her own map and atlas collection. In many cases the librarian can turn to the Internet and locate a map or data set physically located in a library hundreds of miles away. However, this is not always the case. But knowing which collection may contain a needed cartographic item can be a valuable first step in locating the item in question. As map collections everywhere continue to grow, new maps, digital files, aerial photos, and atlases become available to users every day. This detailed, timely, and reliable guide to these varied and still somewhat "hidden" cartographic collections--and their personnel--serves as a useful reference tool, especially in this digital age, when library online catalogues are immediately and readily accessible.