This report describes the Patrol Car Allocation Model (PCAM85), a computer program to assist police agencies determine the number of patrol cars to have on duty in each geographic command at different times of the day and week; a user's guide to PCAM is included. Descriptions of the capabilities and uses of the model encompass typical applications, the role of judgment in using PCAM, and the major differences between PCAM75 and PCAM85 (PCAM85 is a modernized version of the original model developed in 1975). The discussion reviews general operation principles, preparation of a data base, data required for each patrol hour, calculation of performance measures, and prescriptive calculations. The user's guide to PCAM opens with an overview of program operation and then specifies how to enter commands, command format conventions, program vocabulary, and command definitions. The guide also explains error conditions and selecting an objective function. The appendixes contain information on PCAM's calculations, PCAM reference sheets, and addresses for further information. A glossary, 19 figures, and a 40-item bibliography are also provided.