It is now apparent that fire once played some role in shaping all but the wettest, the most arid, or the most fire-sheltered plant communities of the United States. Understanding the role of fire in structuring vegetation is critical for land management choices that will, for example, prevent extinction of rare species and natural vegetation types. Pre-European fire frequency can be reconstructed in two main ways. First is by dating fire scars on old trees, using a composite fire scar chronology. Where old fire-scarred trees are lacking, as in much of the eastern U.S., a second approach is possible. This is a landscape method, using a synthesis of physiographic factors such as topography and land surface form, along with fire compartment size, historical vegetation records, fire frequency indicator species, lightning ignition data, and remnant natural vegetation. Such kinds of information, along with a survey of published fire history studies, were used to construct a map of presettlement fire frequency regions of the conterminous U.S. The map represents frequency in the most fire-exposed parts of the landscape. Original fire-return intervals in different parts of the U.S. ranged from nearly every year to more than 700 years. Vegetation types were distributed accordingly along the fire frequency master gradient. A fire regime classification system is proposed that involves, rather than a focus on trees, a consideration of all vegetation layers. From the Introduction...'The primary object of this paper is to construct a map of fire frequency regions of the United States as they existed in one window of time, the era of European settlement. The intention is to begin to visually relate fire history studies across the country in order to further appreciation of the pervasive role of fire in natural vegetation. The secondary objective is to classify fire regimes in terms of their effects on whole vegetation communities: the canopy, midstory, shrub and herb strata.' Abstract reproduced by permission of author.