This exploratory sequential mixed methods study sheds light on the role of first language (L1) in the second language (L2) classroom. The study explored Jordanian English as a Foreign Language (EFL) teachers' (N=7) attitudes toward using Arabic (L1) to teach English (L2) and the perceived functions and/or negative ramifications of such use. It additionally investigated 104 Grades 10 and 11 students' beliefs regarding their teachers' use of L1. The study found that EFL teachers were aware of the importance of minimizing the amount of L1 use which was influenced by the type of lesson and the proficiency level of students. The study suggests that teachers used L1 to achieve six functions in the classroom, but they also believed that L1 overuse may limit L2 development, and it may also have negative affective ramifications. The students' beliefs regarding their teachers' reasons for using the L1 were in line with the teachers'.