This study conducted to provide background data for the systematic development of the library bibliographic component of a national network analyzes the procedures used in producing the National Union Catalog (NUC), the nationwide union catalog in card form maintained at the Library of Congress (LC), and examines the variations found in records as they are integrated into the file. The report discusses NUC operations and workflow, characteristics of reporting libraries, differences in headings between outside reports to the NUC and LC records, and differences in bibliographic description between outside reports to the NUC and LC records. Conclusions for a nationwide database derived from the analysis of processes in the catalog publication division are presented along with recommendations for future investigation. Tables and figures are provided. (FM)