The tragedy of the commons occurs when people pursue their self-interests in using a shared resource and deplete it, thereby compromising their long-term welfare (Hardin 1968). The larger the area shared, the greater the potential for tragedy. The USDA Forest Service is a multiple-use Federal agency that seeks to balance multiple uses of public resources across the Nation while protecting those resources. The agency, facing con-tinual pressure from the public and interest groups to use public resources, has developed a planning process that includes within its framework an important step-monitoring. Monitoring the effects of resource policies and projects on the Nation's resources is criti-cal to maintaining the long-term health, diversity, and productivity of the public's forests and grasslands today and into the future. A well-designed monitoring program avoids the tragedy of the commons. This guide is an invaluable contribution to understanding how to monitor habitats.