The Critical Trends Assessment Program (CTAP) monitors the condition of forests, wetlands, and grasslands throughout Illinois. We assess changes in ecological conditions and the data we collect serves as a baseline for comparing regional and site-specific patterns throughout Illinois. This program, which is supported by the Illinois Department of Natural Resources, is the first statewide comprehensive assessment of its kind. Since 1997, CTAP scientists have conducted surveys at >450 randomly selected sites, >150 each of forest, wetland, and grassland areas, encompassing both public and private lands. The data we collect and analyze is used to help numerous stakeholders understand the current condition of Illinois' ecosystems, and the impacts of past and ongoing changes to the state's natural resources.