Outdoor recreation can take many forms depending on the types of activities, settings, social engagements, equipment, and times chosen by the recreation participant. Recreation can be physically active (for example, hiking) or more sedentary (for example, viewing natural scenery). Many of the activities of interest to the Renewable Resources Planning Act (RPA) Assessment and to assessments of current or future northern forest conditions are classified as "nature-based" in that they are in some way associated with wildlife, birds, streams, lakes, snow and ice areas, trails, rugged terrain, mountains, caves, and other natural outdoor resources or settings. This book discusses outdoor recreation in the northern United States and provides a technical document supporting the northern forest futures project that includes projections through 2060.