A biology teacher's acceptance or rejection of evolutionary theory as a scientifically valid explanation is potentially important to the role that evolution takes in the high school biology curriculum. Due to the nature of available instrumentation, our understanding of teacher acceptance of this complex overreaching biological theory may be incomplete or confounded. This paper describes the development and validation of the Measure of Acceptance of the Theory of Evolution (MATE)—a 20-item Likert-scaled instrument that assesses teachers' overall acceptance of evolutionary theory. Chronbach alpha reliability of the MATE is also reported.