Since their initial publication in 1982, the ACTFL Guidelines and oral proficiency interview (OPI) have enjoyed widespread use by foreign language educators. They have also been the target of much criticism by researchers of second language acquisition and testing. Much of this criticism has focused on validity claims for the OPI. Other research (e.g., Thompson, 1995) has investigated the interrater reliability of the test. This article provides an overview of research (both critical analyses and empirical studies) conducted on the ACTFL OPI and Guidelines from 1990 to present. The author identifies trends in this research, discusses lessons learned from research in other proficiency test areas, and provides recommendations for areas of future study. (Contains 1 table.)