This article reviews research indicating that, under appropriate conditions, students' evaluations of teaching (SETs) are (a) multidimensional; (b) reliable and stable; (c) primarily a function of the instructor who teaches a course rather than the course that is taught; (d) relatively valid against a variety of indicators of effective teaching, (e) relatively unaffected by a variety of variables hypothesized as potential biases (e.g., grading leniency, class size, workload, prior subject interest); and (f) useful in improving teaching effectiveness when SETS are coupled with appropriate consultation. The authors recommend rejecting a narrow criterion-related approach to validity and adopting a broad construct-validation approach, recognizing that effective teaching and SETs that reflect teaching effectiveness are multidimensional; no single criterion of effective teaching is sufficient; and tentative interpretations of relations with validity criteria and potential biases should be evaluated critically in different contexts, in relation to multiple criteria of effective teaching, theory, and existing knowledge.