This study examined the efficacy of using Quizlet, a popular online study tool, to develop L2 English vocabulary. A total of 9 Japanese university EFL students participated in the study. The learners studied Coxhead's (2001) academic vocabulary list (AWL) via Quizlet over the course of 10 weeks. Results of the pre- and post-tests revealed that the learners were able to make statistically significant gains. Moreover, a questionnaire administered by the researcher indicated that the students had positive perceptions of Quizlet to study L2 vocabulary. Specifically, all three constructs studied--perceived usefulness, perceived ease of use, and behavioral intention to use Quizlet--had mean scores greater than 4 on a 5-point Likert scale, indicating a high-level of agreement. Based on these findings, the author supports the use of Quizlet in the EFL classroom.