A champion tree - the largest known example of its kind - represents the maximum growth of a species. The Washington State Big Tree Program has registered 1,350 trees, belonging to 869 species or cultivated varieties, that are the largest of their kind in the state. Champion Trees of Washington State documents these trees. Among them are 45 trees acknowledged by the American Forestry Association's National Big Tree Register to be the largest known examples of their kind in the United States. Sections on native and introduced trees provide the general and scientific name, circumference, height, crown spread, and AFA points (a combination of circumference, height, and crown spread), date measured, location (including street address, when relevant), and nominator's name for each champion tree. Photographs of 90 trees are included. A discussion of tree measurements explains how to measure and nominate a tree, and a list of former record trees documents trees that would be current champions had they not died or been cut. Indexes include general and scientific tree names and names of cities in which champion trees are located. Champion Trees of Washington State will be of interest to landscape architects, gardeners, foresters, and to all who wish to recognize, document, and preserve these majestic examples of biological maturity.