Familiarity with bird vocalizations is an integral part of birding, identification, and understanding behavior. Thus a good sound library is critical for anyone with a strong interest in birds. A suite of CDs, websites, and apps is available to satisfy this need, each with varying geographic coverage, number of vocalizations per species, quality, and overlap in sound libraries. The Cornell Guide to Bird Sounds: Master Set for North America (Master Set) stands apart from other sound libraries in its massive scope, with 4938 recordings of 735 species. Recordings are meant to represent the vocal and nonvocal repertoire of each species, as well as geographic variation and dialects.