In Illinois, school boards that initiate dismissal proceedings against a tenured teacher without a clear understanding of teacher dismissal case law risk the possibility that an underperforming teacher could be reinstated to a teaching position. The purpose of this study was to examine the history, frequency, and legal basis of tenured teacher dismissals in Illinois for the period from 1990 through 2008 in an effort to identify, through quantitative (frequency counts) and qualitative (content analysis) methods, trends and/or patterns in tenured teacher dismissal hearing officer decisions and appellate court cases. The study was a replication, in part, of Paul W. Thurston's 1990 study of tenured teacher dismissal in Illinois. During the period from 1990 through 2008, 62 Illinois school districts dismissed 219 tenured teachers. Of the 219 dismissal cases, hearing officers upheld 142 dismissals (65%) and overturned 77 dismissals (35%). Dismissal cases generally fell into seven distinct categories: insubordination/absence, drug/alcohol misconduct, personal misconduct, sexual misconduct, physical abuse, incompetency, and lack of qualification to teach. Hearing officers tended to uphold a teacher's dismissal if the teacher had been previously warned and/or if the teacher's misconduct had done damage to students or the school. Hearing officers tended to overturn a teacher's dismissal if the school district failed to follow district and/or legal procedures and/or if the district failed to prove the charges against the teacher at hearing. In conclusion, school districts that are willing to accept the time and financial responsibility of dismissing a tenured teacher can effectively do so for certain insubordination, drug/alcohol misconduct, personal misconduct, sexual misconduct, physical abuse, and incompetence offenses. School districts must prove that the teacher's misconduct has done damage to students or the school, and the district should, when possible, issue a warning before attempting dismissal proceedings. School districts must also strictly comply with both district and legal procedures when dismissing a tenured teacher. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]