The purpose of this study was to review legal grounds upheld by federal and state courts in cases involving the dismissal of tenured public school teachers for alleged incompetence from 1958-1982 to determine a judicial definition of teacher incompetence. In addition, the study attempted to provide an historical analysis to determine if the reasons that federal and state courts have upheld for the dismissal of tenured public school teachers have changed or remained the same since 1958. Third, the study identified in recurring categories behaviors and actions of tenured public school teachers that courts have upheld as evidence of incompetence. Finally, the study sought to be of service to boards of education and professional administrators of the public schools by bringing to their attention the behaviors and actions of tenured public school teachers that courts have upheld as evidence of incompetence that justifies dismissal. Court decisions related to the topic"Teacher Incompetence" were located under the topic"Schools and School Districts" in the Century, Decennial, and General Digests. Cases were reviewed to determine if they fit within the delimitations of the study. Then each case was analyzed in chronological order to see if historically, there had been changes in legal interpretations of evidence that was substantiated by the federal and state courts as definitions of teacher incompetence for tenured public school teachers. Next, the behaviors and actions of public school teachers involved in such cases were divided into categories. Within each category, the specific teacher behaviors were listed according to state and frequency of incidence. These categories included: an inadequate preparation to teach, teaching methods, effect on pupils, personal attitudes, and disability. This research reveals that courts are stating that the incompetent teacher is one who lacks an adequate professional preparation to teach, is unable to provide designated instruction in an appropriate learning environment, and/or exhibits unprofessional behavior such that .the teacher's on-the-job duties cannot be continued successfully. / Ed. D.