The ability to think critically is essential if individuals are to live, work, and function effectively in a current and changing society. As adults, students will be living in a complex world and in a democracy where both individual and collective actions will require effective selection, processing, and use of information. National, state association, business, and industry reports on education produced in the 1980's called for increased emphasis on higher-order learning skills, including critical thinking skills. This digest includes: (1) a definition of critical thinking; (2) research findings concerning critical thinking; (3) a discussion of the role of environmental education in critical thinking instruction; (4) materials available for environmental education that emphasize critical thinking skills; and (5) assistance available to teachers wanting to modify instruction to emphasize critical thinking skills. A list of 14 references is included. (CW)