 The major aim of this study is to provide a better understanding of attempts to stop or reduce marijuana use that can be used to develop better behavioral treatments for marijuana dependence. The application will focus on adult daily marijuana users who try to stop or reduce their marijuana use in a real-world setting. Although prospective, natural history studies describing attempts to stop or reduce alcohol, heroin and tobacco use have proved useful, we know of no such study among adult marijuana users. Two pilot studies will develop measures and assess compliance with our procedures. The main study will recruit up to 400 adult marijuana smokers with the goal of a sample size of 200 participants with adequate compliance. Participants will call an Interactive Voice Recording IVR system daily for 3 months to report marijuana use, quitreduction attempts, and events that might increase or decrease the probability of initiating a quitreduction attempt or the success of an attempt. Follow-up at 6 months will track recent marijuana and other drug use. Knowing what motivates marijuana users to try to stop or reduce, and knowing which strategies for stopping marijuana use are successful, can help develop treatments for marijuana dependence. For example, if stopping tobacco when trying to stop marijuana decreases the chance of stopping marijuana, then smoking cessation should be done after stopping marijuana. Or if reducing marijuana often leads to cessation, then convincing those not interested in quitting marijuana to first try reducing may be helpful. 