This chapter sets out to give an introduction to the blended language learning (BLL) research domain through an analysis of the most impactful BLL research as measured by Harzing’s Publish and Perish software. After an initial outline of the field of BLL and its development, the chapter discusses the research methods and approaches applied in the selected articles and demonstrates that a majority of the articles use a descriptive approach and the dominating method is interpretative studies. The chapter then goes on to analyse the themes of the articles and divides them in to six sections: students’ readiness for BLL, teachers’ perceptions of BLL, learner autonomy and self-regulated learning, second language acquisition, technology and BLL design. Finally, we offer future research directions in order to increase the sustainability of BLL, both as the field of practice and the research area. Overall the 41 reviewed studies present a substantial case for the benefits of BLL. However, to ensure the sustainability of BLL design and thus the generalisability of the research findings further BLL designers and researchers need to apply firm theories.