In the second language classroom, the teacher's speech constitutes a critical source of second language (L2) input for learners. Previous research has supported the judicious use of the learners' first language (L1) in teachers' speech to increase the comprehensibility of the input; however, L2 teacher training programs and educational policies often discourage their use of the learners' L1. The present study was conducted in Quebec. It investigated the relationship between secondary school English second language (ESL) teachers' reported amount of in-class use of the learners' L1 (French) and the variables of teachers' proficiency in English, confidence with English, beliefs about language use, learners' age, learners' ability level, school setting, and compliance with the 'English only' recommendation from Quebec's ministry of education.  Sixty-six teachers completed a questionnaire, and 6 also participated in interviews. The results indicate that there is a significant relationship between the reported amount of French used in class (0-80%) and the language use beliefs of the teachers. There was some evidence of learners' age and learners' ability level influencing teachers' use of French. Neither teachers' English language proficiency nor confidence with English was strongly related to the reported amount of French used. The findings from this research have implications for language teaching and language teacher training in Quebec and elsewhere.