Digital materials are reshaping library collections and, by extension, traditional library practice for collecting, organizing, and preserving information. This paper uses OCLC's WorldCat bibliographic database as a data source for examining questions relating to digital materials in library collections, including criteria for identifying digital materials algorithmically in MARC21 records; the quantity, types, characteristics, and holdings patterns of digital materials cataloged in WorldCat;

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... d trends in WorldCat cataloging activity for digital materials over time. Issues pertaining to cataloging practice for digital materials and perspectives on digital holdings at the work level also are discussed. Analysis of the aggregate collection represented by the combined digital holdings in WorldCat affords a high-level perspective on historical patterns, suggests future trends, and supplies useful intelligence with which to inform decision making in a variety of areas. The authors wish to thank several anonymous reviewers for their extremely useful comments and suggestions.