This study examined 34 Head Start teachers' use of four categories of mental state talk (verbalizations of mental processes using emotion terms, cognition terms, desire terms, and perception terms) during naturally occurring classroom interactions. Transcriptions from classroom videos were coded for mental state talk category, sentence type in which the mental state term was used, and referent of the mental state term. Results indicated that teachers used varying amounts of mental state talk (perception terms were used most frequently and emotion terms least frequently) and that categories of mental state talk differed by sentence type and referent; emotion and cognition terms were used in statements more than questions, and, when using emotion terms, teachers were more likely to refer to their own emotions than children's emotions. Differences in teachers' mental state talk were associated with teachers' years of experience and observed classroom quality as assessed by the Classroom Assessment Scoring System. Practice or Policy: Teachers' mental state talk may be a mechanism through which teachers' use of verbal language contributes to positive and sensitive teacher-child interactions. Further examination of mental state talk within teacher-child interactions has the potential to contribute to understanding aspects of effective teaching in early childhood classrooms. (author abstract)