A lapse refers to an initial episode of substance use following a period of abstinence. A lapse may or may not lead to more substance use. Clients always run the risk that a lapse will turn into a relapse, in which they continue to use alcohol or other drugs. A lapse or relapse is the last link in a chain of decisions, and how one responds to an initial lapse has a big impact on whether or not one has a full-blown relapse. The goals of this chapter are to understand the difference between lapse and relapse, to learn about relapse prevention strategies, and to learn to identify and manage relapse warning signs and high-risk factors.