This fire regime synthesis details characteristics of ponderosa pine ecosystems from fire history studies conducted in two ecoregions in New Mexico: the Southern Rockies ecoregion (hereafter, Southern Rocky Mountains) and the Arizona/New Mexico Mountains ecoregion (hereafter, New Mexico Mountains). Together, fire frequency, fire severity, fire extent, fire seasonality, and the fire-climate relationship provide a cohesive interpretation of the dominant historical fire regime (i.e., prior to Euro-American settlement) and how the contemporary fire regime differs. Fire frequency data were obtained from 108 sites using fire scars dating from 1513 to 1993. The overall mean fire interval (MFI) was 9.3 years (n = 108 sites) with very low variability among sites (SE = 0.58 years). Fire frequency and site elevation were weakly correlated (r = 0.18), and although the slightly higher elevation Southern Rocky Mountain sites had a longer mean fire interval (mean elevation = 2,540 m, MFI = 11.2 years, n = 54 sites) than the New Mexico Mountains sites (mean elevation = 2,386 m, MFI = 7.3 years, n = 54 sites), the difference was not statistically significant. The vast majority of evidence shows fires were frequent (94% of sites had MFI < 20 years), which strongly suggests that low-severity fires were the dominant type. Higher severity fires occurred less frequently - particularly during extended periods of drought or during severe drought. These droughts were also associated with widespread fire years. Most historical fires seem to have occurred in spring and early summer, prior to the onset of monsoon rains. Most fire scars from 9 sites in the Southern Rocky Mountains and 21 sites in the New Mexico Mountains were in dormant and early earlywood positions (min 51%, max 97%, mean 69%, n = 8 studies), which are attributed to fires occurring between April and June. Fire seasonality data spanned six centuries (from 1296 to 1903), suggesting a persistent relationship between pre-monsoonal dry conditions and early season lightning ignitions. The fire-climate relationship was similar between the two ecoregions with all results indicating drier-than-average conditions during the fire year and wetter than-average conditions dominating in the 4 antecedent years. The pattern of wetter-than-average conditions in the immediate years preceding a fire year is 3 Fire Effects Information System (FEIS) indicative of a fuel limited system, whereby biomass production that results from increased moisture availability is desiccated and burned in subsequent drier-than average fire years. The dominant fire regime characterized by frequent, low-severity fires has shifted to less frequent and higher severity crown and stand-replacing fires over recent decades. Both the area burned at high severity and the percentage of high severity fires increased in New Mexico ponderosa pine forests from 1984 to 2015.