Job analysis interviews were conducted with a sample of nine Illinois police chiefs as the basis for developing a job analysis questionnaire to be administered statewide. The questionnaire sought information on demographics, tasks and activities, knowledge areas, skills, abilities, and other personal characteristics; it also contained an open-ended question and comment section. Questionnaires were sent to 500 police chiefs, all of whom were members of the Illinois Association of Chiefs of Police; 122 questionnaires were returned. Data suggested that the prototypical police chief was a white male in his 40's, with experience in patrol and investigative activities, about 20 years of experience as a Certified Law Enforcement Officer, about 7 years of experience as a police chief, and the equivalent of about 3 years of college. While duties and responsibilities differed to some extent at the task level, there was substantial overlap among police chiefs of different department sizes in the knowledge areas required and the skills and abilities required to successfully carry out the department's mission. Police chiefs determined that it was essential to have general knowledge of patrol and investigative functions in police work, as well as general knowledge of the criminal justice system. Possible uses of the data are discussed in the context of a voluntary certification process for police chief candidates. 11 notes and 14 tables