Co-teaching is a widely implemented instructional strategy that poses unique challenges to teachers and may require targeted training. This study considers the role of pre-service and in-service professional development opportunities regarding co-teaching and teacher confidence, interests, and attitudes regarding co-teaching in a sample of general education and special education teachers. After controlling for key teacher demographics, professional development opportunities around co-teaching were positively associated with each teacher outcome. Teachers with more frequent in-service opportunities in co-teaching were more confident in their co-teaching practice and demonstrated higher levels of interest and more positive attitudes about co-teaching than did those teachers with less frequent in-service opportunities. Pre-service training on co-teaching was also positively associated with teacher confidence. (Contains 6 tables and 1 note.)