Recent estimates indicate that nearly 40.5 million ha (100 million ac) of forest lands that were historically burned by frequent surface fires in the western United States may benefit from the restoration of surface fire. An additional 4.5 million ha (11 million ac) of forests need to be treated to protect communities from wildfire (Aplet and Wilmer 2003). Rummer and others (2003) estimate that over 26.7 million ha (66 million ac) of forestlands could benefit from fuel reduction. Even with uncertainties in these estimates and arguments as to their precision and accuracy, they clearly illustrate the staggering number of hectares (acres) that need fuel treatments in order to modify fire behavior and burn severity. Access and operability issues further limit the options available on a large portion of western forests. Costs and lack of industrial infrastructure to use small diameter material are other critical factors influencing treatment possibilities. We, the authors, recognize that theoretically, all forests of the western United States could be treated in one way or another to modify wildfire behavior and burn severity. Many of the principles and concepts we discuss are relevant for fuel treatments within other forests and locales; however, we will emphasize forest treatments applicable for use in the cold, dry, and moist forests of the inland western United States. We will discuss forest treatments that influence watershed processes, defined as those that occur when water transports sediment, woody debris, chemicals, heat, flora, or fauna away from a site and deposits it on another site. We define a cumulative effect as one that results from the incremental effects of an event when added to other past, present, and reasonable projected future effects regardless of the triggering action or event (Reid 1988).