Constraints on the thermochronologic evolution of the New York crystalline basement are mainly restricted to the high-temperature early cooling history following 1.1 Ga Grenville metamorphism (U-Pb methods) and the late cooling history (fission track methods). The thermal history for the ~one billion years between these intervals is herein assessed using 40Ar/39Ar hornblende, muscovite, biotite and K-feldspar thermochronology. Hornblende preferred ages suggest cooling below ~450--500 ¿C between ca. 900 and 950 Ma. Total gas ages of biotites range from ~746--1060 Ma, and their age spectra complexity is probably related to younger thermal events and/or excess argon. A single muscovite analysis yields a preferred age of 854 Ma. Argon isotope analyses of K-feldspar provide a quantitative evaluation of the thermal history between ~175 and 350 ¿C. Multi-diffusion domain thermochronology on highly variable K-feldspar results yield internally consistent thermal histories and, along with geologic constraints, suggest thermal maxima of 275--350 ¿C at ca. 700, 470--450 and 300 Ma. Combining all of the K-feldspar analyses provides an internally consistent thermal history for the region and allows for the following inferences. Reheating at ~700 Ma associated with Late Precambrian rifting during the formation of the Iapetus ocean apparently affected the entire Adirondack region with the highest temperatures occurring in the eastern part of New York. Local reheating in the Ordovician is inferred to have affected the eastern Adirondack Mountains and probably resulted from the combined effects of burial during the Early Paleozoic, emplacement of Taconic thrust sheets and migration of hot fluids along normal faults during the Taconic orogeny. High paleotemperatures for the Devonian section of eastern New York are related to maximum burial of the basement during the Carboniferous at ca. 300 Ma. ¿ 1998 American Geophysical Union