Learners’ self-efficacy plays a crucial role in achieving success in second language (L2) acquisition. As a determinant of success and failure, self-efficacy should be measured appropriately and effectively using empirically and theoretically based instruments. Many of the current measures, however, are either not necessarily designed to assess self-efficacy in L2 learning, or they are lengthy, making them impractical to use alongside other instruments. The purpose of this study was therefore to develop and validate a new 11-item Questionnaire of Self-Efficacy in Learning a Foreign Language (QSLL). In Study 1, the initial items were piloted with 323 English as a foreign language (EFL) learners from three universities in Turkey. In Study 2, a revised version of the questionnaire was administered to 701 EFL learners from an additional three Turkish universities. The analyses supported a bifactor model over the other four models tested. The bifactor model had one general L2 self-efficacy factor that underlined each of the items. Separately, there were two specific factors, namely L2 reception (i.e., reading and listening) self-efficacy and L2 production (i.e., speaking and writing) self-efficacy. Empirical evidence supporting measurement invariance and predictive validity were also provided. Overall, the results show strong evidence for the reliability and validity of the QSLL. Implications for research and practice are discussed.