Millimeter-wave backscatter measurements are presented for various tree types taken during the 1987 growing season at Amherst, Massachusetts. These measurements were taken with a 215-GHz radar system that is capable of measuring backscatter for the VV (vertical transmit, vertical received), HH (horizontal transmit, horizontal received), VH, and HV polarizations. Geometrical optics modeling was used for the normalized radar cross section (RCS) of deciduous trees and the backscatter is shown to be characterized in terms of gravimetric leaf water content, the leaf area, and the foilage crown cover. Data are also provided for coniferous trees, although the geometrical optics model is not applicable in those cases. >