Although use of machine translation (MT) technologies by learners may seem like a relatively new issue in foreign language (FL) education, researchers have been investigating connections between MT tools and FL teaching and learning for more than three decades, years before learners had access to free online services such as Google Translate. This literature review summarizes this rapidly expanding research domain both chronologically and thematically, identifying key concepts, insights, and findings and mapping them onto a framework inspired by questions commonly asked by both researchers and practitioners: How do learners use MT tools? What do instructors and learners think about MT? How might MT use affect language learning? How should instructors respond to MT use by learners? By summarizing and drawing connections between the assumptions, methods, and findings of key studies in these categories, this review provides a historical perspective and suggests new directions for future research.