Our theory of drug use is one which centrally posits that drug-taking behavior is caused by several large constellations of intra- and extra-individual forces. These domains of influences interact to modify each other while determining the presence or absence of a large variety of lifestyle behaviors including drug and alcohol use. Many previous theories of drug-taking have provided valuable 12contributions to the field in that they are correct as far as they go; flaws in these theories stem less from incorrectness than from the pragmatic consideration that attention has been focused on one set of forces to the exclusion of other domains of influences. In order to provide a more comprehensive view of drug use than is typical, we will discuss the models or domains of influences which form major subsystems in our larger theory, and then present more specific ideas on how different influences work to modify each other as well as to determine the performance of behaviors.