This paper presents a model of the programming process. The model has four parts. A resources model specifies how many useful man-months of design effort are available from project team members after subtracting the time required for learning and team communications. A system design model specifies how many man-months of effort are required to derive program module specifications, as a function of the number of team members, program size, and number of modules. A coding model specifies how many man-months of effort are required for coding, as a function of team, module, and program size. Finally, a checkout model specifies how many man-months are required for checkout as a function of program size, error detection and correction rates, and a design-complete factor. The model as a whole predicts that programmer productivity will decrease as project team size is increased and that project duration will first decrease and then increase as team size is increased. It also shows that productivity and project duration vary enormously as a function of project management factors, even when project complexity and programming staff competence are held constant.