This paper develops definitions for a program schema, the execution of such a program schema, and a process generated by a program schema. Results due to Hartfiel are used to characterize the cone of stochastic eigenvectors of the class of homogeneous Markov processes generated by a program schema. The stochastic behavior vector of a process generated by the same schema is shown to lie in this cone. In the case of a cyclic structured program schema, all of the vertices of the base of the cone are exactly generated by the circuits of the schema. Some directions for future work are suggested.