This well-written biography of outstanding climatologist C. Warren Thornthwaite (1899-1963) was written from unpublished letters and other accounts by his contemporaries, and includes a complete bibliography of his published works. For both general readers and specialists, it traces the chronology of Thornthwaite's achievements and his relationships with other important figures in American geography. Thornthwaite's Laboratory of Climatology, located in a farm setting at Seabrook and later Centerton, New Jersey, was a mecca for climatologists from all parts of the world. His most important scientific contributions were his new, "rational" classification of world climates in 1948 and his concept of evapotranspiration and its use in climatic water budget. Having recognized that the relative moistness or dryness of a climate can only be determined if one compares precipitation with potential evapotranspiration, Thornthwaite compared supply with demand on a daily, monthly, and annual basis and was able to obtain quantitative values of such factors as water runoff, irrigation need, and water storage in the soil. Climatologists, hydrologists, and agriculturalists all have been touched by Thornthwaite's innovations. This engaging account of his achievements and his personal life explores his methodology and places his work in the perspective of his times.