The question of whether a library's catalog should consist of cards arranged in a single alphabetical order (the "dictionary catalog) or be segregated as a separate file is discussed. Development is extended to encompass related problems involved in the creation of a book catalog. A model to study the effects of congestion at the catalog is created. Using a drawer chosen randomly from either a dictionary catalog, or the subject or author-title part of a split catalog, three measures of congestion are considered: (1) the probability that the drawer is being used, (2) the average time needed to wait for a use and (3) the average number of people attracted to the drawer at any time. All the parameters used and the basic relations among them are collected in Section II. The first measure of congestion considered is the likelihood that a user must wait before he can use a drawer. The next measure of congestion is the mean time a user must wait to gain access to a drawer. The final measure of congestion is the number of people contributed to the system at any time along each drawer. Section VI considers the implications of the model for the construction of book catalogs. It was found that each of the three criteria of congestion can lead to a different conclusion. (Author/NH)