The ultimate task of prevention is creating healthy environments for youth. Community and larger systems influences can work to support or to undermine prevention efforts targeted to individuals, families, the peer group, and schools. Successful community prevention planning is collaborative, involving the people who live in, work in, or serve the community with a stake in the resolution of the problem. Addressing the community environment itself can be a powerful strategy to limit problems related to the use of alcohol and other drugs among youth. There are three general areas in which effective intervention can occur: availability of alternative activities for youth; availability of alcohol and other drugs to youth; and the normative environment of the community as it relates to the use of alcohol and other drugs. Three projects, the Bayview Hunter's Point Prevention Project, Crossroads, and the Castro Valley Prevention Planning Project, provide excellent examples of the kind of community-based, environmentally-focused prevention planning that can occur. 17 references.