Fire is a primary natural disturbance in most forests of western North America and has shaped their plant and animal communities for millions of years. Native species and fundamental ecological processes are dependent on conditions created by fire. However, many western forests have experienced shifts in wildfire regimes and forest structure following a century or more of resource use and management, with some past and present management activities lacking a scientific basis. Changes in wildfire and fuel management policies are needed to address social and environmental problems that have arisen as a result of these activities. Incorporation of current scientific knowledge into revised policies and practices is essential to insure that the productivity, biological diversity, and ecological values of western forests are sustained. As an example, implementation of the Healthy Forests Restoration Act (HFRA) of 2003 will benefit from adaptive application of the dramatically expanding base of scientific knowledge. Our review addresses the ecological science relevant to developing and implementing forest restoration and fuel management policies, including activities conducted before, during, and after forest wildfires. An essential principle of ecological variability within and among forests underlies all of our findings. In this summary and in the background report we use the term 'characteristic' in referring to the dominant natural disturbance regime of a forest type or site. For example, some types of dry forests are described as being historically or naturally 'characterized by a frequent, low-severity fire regime' while some coastal and sub-alpine forests are 'characterized by an infrequent, high-severity fire regime.' These are generalized characterizations of the regimes that these types experience and are not necessarily exclusive. For example, forests characterized by high-severity fire regimes may also experience low-severity events and vice versa. The term 'uncharacteristic' refers to disturbances, forest structure, or fuel loads of a scale or type outside the historic range of variability based on site-specific vegetation reconstructions using tree rings, fire scars, pollen, charcoal, or early historical records.