Applied linguists' interests and values have expanded in synergy with evolving technologies over the past decades, and with the tools and concepts developed in other disciplines. This timely book explains applied linguists' interest in technology in connection with their study of language-related problems in the real world. The decades of history and intersections with other disciplines provide background for introducing 11 types of technology-mediated language learning activities, grounded in the research-practice interface characterizing applied linguistics. Examples of past research are interpreted through the lens of design-based research to examine how design principles are developed for language learning and language assessment. Concrete implications are outlined for language pedagogy and its evaluation, language teacher education, and technology studies in applied linguistics. These foundations of technology and language learning will animate a spirit of critical professional inquiry toward current and future digital technologies as they intersect with language learners.