The reliability of the ACTFL Oral Proficiency Interview (OPI) has not been reported since ACTFL revised its speaking proficiency guidelines in 1999. Reliability data for assessments should be reported periodically to provide users with enough information to evaluate the psychometric characteristics of the assessment. This study provided the most comprehensive analysis of ACTFL OPI reliability to date, reporting interrater consistency and agreement data for 19 different languages. Overall, the interrater reliability of the ACTFL OPI was found to be very high. These results demonstrate the importance of using an OPI assessment program that has a well-designed interview process, a well-articulated set of criteria for proficiency determination, a solid rater training program, and an experienced cadre of testers. Based on the data reported, educators and employers who use the ACTFL OPI can expect reliable results and use the scores generated from the testing process with increased confidence. Recommendations for future research are discussed. (Contains 4 tables.)