This paper reviews briefly the climatic and edaphic factors related to tree adaptation. Photoperiod regimens, the timing and severity of low temperatures, and high temperaturemoisture interactions all are important climatic determinants of adaptation for which adequate data have been widely recorded. Edaphic factors that injure trees in managed environments are more difficult to extrapolate to natural systems, but natural soils that are poorly drained, calcareous, alkaline, or saline may be initial foci for seeking tough trees. A project to identify promising new landscape plants for the north-central United States, by examining climatic, edaphic, and floristic factors in Eastern Europe, is presented as a case study.