An algorithm is presented for the special integer linear program known as the set partitioning problem. This problem has a binary coefficient matrix, binary variables, and unit resources. Furthermore, all of its constraints are equations. In spite of its very special form, the set partitioning problem has many practical interpretations. The algorithm is of the branch and bound type. A special class of finite mappings is enumerated rather than the customary set of binary solution vectors. Linear programming is used to obtain bounds on the minimal costs of the subproblems that arise. Computational results are reported for several large problems.