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 continual 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 critical 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.