This qualitative study sets out to understand the beliefs, functions, and practices of using L1 among EFL learners while they learned new L2 vocabulary. Forty-two Saudi male university students were randomly assigned to 21 pairs and asked to complete three reading comprehension tasks. All pair interactions were audio-recorded. Afterward, interviews were conducted with 21 students. The results suggest that the use of L1 in L2 vocabulary tasks assists students in understanding the meaning of new words. They also revealed the complex sociocultural nature of peer-to-peer collaborative interaction and the role L1 plays in L2 vocabulary learning. The interviews revealed that some participants thought that L1 should not be used in the L2 class, a belief that contradicted their actions. The paper calls for Saudi L2 educational contexts to embrace translanguaging as a beneficial practice that enhances student L2 acquisition and reduces the emotional stress of using L1 in the classroom.