This article examines definitions state education agencies use to describe the federal education disability called “emotional disturbance.” State definitions were collected so that various aspects of them could be analyzed and compared with results of similar studies completed in the 1970s and 1980s. Among results are that state definitions have changed substantially over the decades and definitions have become increasingly similar to the federal definition. Discussion elaborated key findings about components of the state definitions, changes in terminology, and features of the federal definition shared by state definitions. Several recommendations are offered for research and policy consideration, as suggested by the findings.