International Index to Music Periodicals, Music Index Online, and RILM Abstracts of Music Literature are the principal databases for music research. While similarities exist between these databases in terms of titles indexed, as well as in terms of the depth and extent of coverage, the differences are significant. An understanding of indexing practices will influence subscription decisions and the selection of databases for particular research needs. One measure of the effectiveness of an index is the comprehensiveness of its indexing; that is, the extent to which single issues are analyzed. In this study six widely-subscribed music periodicals were exhaustively searched in all three indexes. In addition to typographical errors, spelling errors, and incorrect page numbers, all three databases exhibited significant lacunae, technical problems that interfere with data retrieval, and less-than-precise claims for coverage.