Using the mother tongue (MT) in English as a foreign or second language (EFL/ESL) classrooms is indispensable, especially in beginner classes. This paper aims to add to the present literature on this issue by highlighting the attitudes of both students and teachers towards MT use in English as a foreign language (EFL) classroom, the justifications for its use, and some of the actual interaction practices in grammar classes. It investigates the attitudes of 110 Saudi EFL female beginners and their two teachers toward using the Arabic language in EFL grammar classes at Jazan University. It also investigates the students’ reasons for using or avoiding their MT. Moreover, it presents some of the functions that MT serves in EFL grammar classes. To collect the data, the researchers used two questionnaires and classroom observations. For data analysis, they used Microsoft Excel and thematic content analysis. The results indicated that, although both students and teachers generally have positive attitudes toward using the MT in EFL classes, they are also aware of the adverse effects of its overuse. The results also revealed that the teachers and students use MT in EFL classes to serve different classroom functions that ease the teaching and learning processes. Based on these findings, the study provided recommendations for teachers, curriculum designers, and future researchers.