Fuel treatments have become an indispensable tool for managing fire in North American wildland ecosystems. Historical perspective and extant practices provide insights into current theory and areas of future emphasis. Managers have better understanding of treatment practices as researchers have provided clearer understanding of fire behavior in treated vs. untreated areas and enhanced wisdom about ecological effects in a variety of fire regimes. Even so, recent breakthroughs in the theory and practice of fuels management have been limited, and significant knowledge gaps remain, particularly fuel and treatment quantification. In general, the theory behind fuel treatments has lagged actual practice as implementation has preceded scientific understanding. Until the late twentieth century, fuel hazard reduction was considered incidental to forest management activities such as timber harvesting (exception: southern California and other shrubland ecosystems). Fuel treatment usage has expanded in response to devastating wildfires despite limited insights regarding effectiveness. Extant procedures for analyzing treatment efficacy (i.e., computer modeling, retrospective analyses of wildfires encountering treated areas, and experimentation) likewise suffer from analytical shortcomings. Fundamental questions related to efficacy remain, especially linkage to treatment objectives as affected by fire behavior, treatment intensity, and values at risk. Future research needs include a generalized, cohesive theory on the role of fuels in combustion dynamics, and improved effectiveness metrics at project and landscape scales.