Codeswitching is reported to be a common feature of group work in EFL classes, particularly those with learners sharing the same native language. On the other hand, there is little research on codeswitching in group work in EFL contexts. This study aims to investigate the reasons why codeswitching is employed in EFL group work interactions among learners who share the same native language. The data were collected via observations of group work processes and open-ended questionnaires given to the students and thematically analysed. According to the findings, codeswitching in group work served mainly four types of purposes: i) search for equivalence, ii) meaning clarification, iii) following task procedure and iv) emotional expression. The task type being a spontaneous speaking task or an outcome production task and the students' being in an on-record or off-record mode also affected the extent of codeswitching. Another finding was that the instructor's use of L1 in the classroom might derive students to switch codes. The students reported that they switched from English to their native language particularly due to their lack of proficiency and the fact that they found L1 communication a convenient way of expressing their concerns and emotions. Codeswitching was found to be a builder of solidarity and a means of achieving task targets as well as interactional fluency, implying that it can serve pedagogically useful purposes in group work in EFL classes.