Decriminalization legislation may be introduced into a system characterized by a consensual system of values opposed to marijuana use, a severe system of legal sanctions for violations of consensual values, and a system of informal sanctions similarly reflecting a rejection of marijuana use patterns. Under such a system, decriminalization could increase marijuana use by legitimizing its use and minimizing prior presumed harmful effects, decreasing the range of formal and informal sanctions for marijuana use, and failing to deter those who desired to use marijuana but were constrained by conditioning to obey the letter of the law. A decrease in marijuana use could result under such a system because of bringing marijuana use out into the open and increasing contact between users and persons carrying dominant social values against its use, thus increasing the impact of informal sanctions against marijuana use, as well as diminishing the excitement of an act that formerly violated formal laws. Under conditions where decriminalization expressed popular social values, a decrease in marijuana use might also follow decriminalization, particularly where the contranormative nature of the act was the earlier basis for its performance (i.e., where the motivation to use marijuana was to express antiauthority attitudes or other contranormative stances). Finally, where decriminalization was merely the reflection of preexisting social attitudes, it might be expected that the consequent widespread prevalence of the act would preclude further appreciable increases in marijuana use by virtue of a ceiling effect. The theoretical models are graphically illustrated, and 18 notes are provided.