In 2005, 40 new fire behavior fuel models were published for use with the Rothermel Surface Fire Spread Model. These new models are intended to augment the original 13 developed in 1972 and 1976. As a compiled set of quantitative fuel descriptions that serve as input to the Rothermel model, the selected fire behavior fuel model has always been critical to the resulting modeled fire behavior. Fuel characteristics affect both the heat source and the heat sink factors in the spread model. While the original 13 models emphasized peak fire-season fuel combinations, the new set establishes a greater role for live fuels. Use of live fuel as a variable produces a broad range of modeled fire behavior related to seasonal vegetative development, especially for those fuel models that include herbaceous fuel loads. Intending to represent 'greenup' and late season 'curing,' the new fuel models allow the user to transfer herbaceous fuels from live to dead. As fuel load transferred increases, the influence of moisture of extinction and wind limit produce dramatic changes in modeled spread and intensity. The new models present an important opportunity to model fire behavior under a wider range of fuel conditions, including fire use. However, the user needs to be aware of the live fuel components in the selected models and manage those inputs carefully.