With the popularity of translanguaging recently, the use of L1 in EFL setting has been the center of many studies again. This current study takes the topic from a functional perspective and looks at the use of L1 at an English-medium university in Turkey from a functional interactional point of view. The data is taken from recorded classroom data, further triangulated by focus group meetings. Two groups of students, namely control and experimental, were recorded during pair work and their L1 uses were analysed based on students’ proficiency levels and the functions L1 instances served. The findings suggest that students resort to their mother tongue during interactive class tasks mainly for task-related issues and social purposes. Furthermore, results also demonstrate that weaker students tend to refer to their native linguistic resources more to make sense of the task and achieve the task, whereas stronger students use their L1 more for social interaction purposes.