The National Wildfire Coordinating Group (NWCG) definition of extreme fire behavior (EFB) indicates a level of fire behavior characteristics that ordinarily precludes methods of direct control action. One or more of the following is usually involved: high rate of spread, prolific crowning / spotting, presence of fire whirls, and/or strong convection column. Predictability is difficult because such fires often exercise some degree of influence on their environment and behave erratically, sometimes dangerously. Alternate terms include blow up and fire storm. Examples of historic wildland fires that resulted in loss of life and/or extensive property or ecological damage through what qualifies as EFB include: the 1871 Peshtigo Fire, the 1910 Great Idaho wildfires, 1949 Mann Gulch Fire, the 1988 Yellowstone NP Fires, South Canyon Fire of 1994, and 2001 Thirty-Mile Fire. Instances of EFB are well documented throughout history, and EFB will continue to be a control and safety problem on wildland fires in the future. Fire managers examining these and other fires over the last 100 years have come to understand many of the factors necessary to EFB development. This work produced guidelines such as the Byram reverse wind profile, Rothermel's plume-dominated versus wind-driven fire classification dichotomoy and his crown fire model, and the Haines Index. This information is included in current firefighter training which consists of: an introduction to EFB in S-290 (Intermediate Wildland Fire Behavior) and the core concepts in S-390 (Introduction to Wildland Fire Behavior Calculations), which are expanded upon in S-490 (Advanced Wildland Fire Behavior Calculations). Through progression of this coursework, concepts are used, understood, and reinforced. These courses present the current methods of predicting EFB using the crown fire model, which is based upon the environmental influences of weather, fuels and topography. Current training does not include the full extent of scientific understanding. For example, Byram's analysis that produced the adverse wind profile included aspects related to wind direction as it depended on height, but this is not discussed in the research or training literature. Material in current training programs is also not the most recent scientific knowledge. National Fire Plan funds have sponsored newer research related to wind profiles' influence on fire behavior, plume growth, crown fires, fire dynamics in live fuels, and conditions associated with vortex development. A point of significant concern is the fact that characteristic features of EFB are intrinsically dependent on conditions undetectable on the ground, depending fundamentally on invisible properties such as wind shear or atmospheric stability. Obviously no one completely understands all the factors contributing to EFB due to known and implicit gaps in our knowledge. These gaps, as well as the limitations as to when various models or indices apply should be noted and acknowledged to avoid application where it is not appropriate or warranted. This synthesis will serve as a summary of existing extreme fire behavior knowledge for use by fire managers, firefighters, and fire researchers. The objective of this project is to synthesize existing EFB knowledge in a way that connects the weather, fuel, and topographic factors that contribute to development of EFB. This synthesis will focus on the state of the science, but will also consider how that science is currently presented to the fire management community, including incident commanders, fire behavior analysts, incident meteorologists, NWS office forecasters and firefighters in the field. It will seek to clearly delineate the known, the unknown, and areas of research with the greatest potential impact on firefighter protection.