Language learners in higher education increasingly use out-of-class self-directed learning facilitated by mobile technology. In order to make informed educational decisions, this study sets out to provide an overview of empirical research into learning strategies that self-directed learners use with the support of mobile technology in language learning. Twenty studies were selected and systematically analysed, revealing the cognitive, metacognitive, social and affective strategies that self-directed learners used in their language learning processes. Low-cognitive strategies appeared to be more commonly reported than high-cognitive strategies. The use of metacognitive strategies was more closely associated with the forethought phase and performance phase than with the self-reflection phase, yet only a few articles reported all three metacognitive phases. Three kinds of social strategies were examined, and only one affective strategy was reported. Finally, implications of these findings and directions for future research are provided for self-directed learners, practitioners and researchers to facilitate self-directed learning and future work.