The Library Catalog Cost Model described in this report was developed to assist each of the 72 individual libraries participating in the project to compare the costs of alternative future forms of the catalog, emphasizing the costs of implementing AACR 2 (Anglo American Cataloging Rules 2). Inputs characterizing their costs and modes of operation were prepared by 68 libraries. These inputs were used to compute, by means of the model, costs of alternative forms of the catalog, including card, COM (computer output microfilm), and online. Analyses were performed of the inputs and the outputs of the model, and both were found to be highly variable. Thus it was difficult to draw general conclusions valid for groups of libraries regarding which alternative form of the catalog is the least costly. The costs of implementing AACR 2 were estimated to be of the order of four to seven percent of the total cost of developing and maintaining a catalog. The model may be a useful tool in planning, budgeting, and staffing work at an individual library; furthermore, it may be regarded as a prototype which could be modified to project costs to other library operations, especially acquisitions. Recommendations are presented for future model development. Appendices include edited versions of the basic material sent to participating libraries in July 1979 to assist them in compiling data to input to the Library Catalog Cost Model. Materials include: a background paper; general remarks concerning the model and its inputs; guidance for preparing the input form; input forms; and default figures. Numerous tables and figures are included in the report. (Author/THC)