This brief overview discusses the rationale for measuring teachers' attitudes toward the mainstreaming of handicapped students into regular classrooms, as well as research findings on teacher attitudes. Two attitude tests, Berryman and Berryman's Attitudes Toward Mainstreaming Scale and Hall's Stages of Concern Questionnaire, are also briefly described. The identification of teacher attitudes is important because of the effects of teachers' expectations on students, as well as the relevance of teacher attitudes for evaluating program effectiveness. Teacher attitudes, both toward handicapped students and toward mainstreaming, can be measured by rating scales, interval scales, rank order, Q sorts, semantic differential techniques, sociometric techniques, adjective checklists, questionnaires, and interviews. Research shows that many teachers express negative views about handicapped students and mainstreaming, especially for emotionally disturbed and mentally retarded students. Both support services and teacher education are associated with more positive teacher attitudes. (GDC)