144 12 Case study research Making language learning complexities visible Patricia A. Duff Introduction Case study research has played an important role in applied linguistics for many decades, but it is now enjoying increasing prominence for a variety of reasons. One set of reasons is related to its accessibility, its clarity, its potential impact on readers, and its role in knowledge mobilization and communication with wide audiences. By analyzing and presenting one or a small number of very concrete instances of a phenomenon, within a relevant theoretical framework and research design, researchers can make visible some of the complex dimensions of people’s language-related and social engagements in events that resonate with others. Another set of reasons for its burgeoning role and visibility in publications is that although case studies are not uncommon in research in psychology and other felds traditionally considered more positivist in orientation, the “social turn,” and a greater emphasis on sociocultural dimensions of language learning and use (Duf, 2019), such as learner subjectivity and the “self” in applied linguistics (e.g., Kramsch, 2009; McNamara, 2018), and a focus on identity, ideologies, narrative, and voice, among other dimen- sions of human experience, have rendered case study a highly appropriate approach to research in applied linguistics. In other words, less attention overall is being paid to learners’ linguistic systems (either at one time or over time) and, instead, more attention is paid to their lives and other systems and processes at work in their past, present, and future engagements with language. In this chapter, I discuss the core features of case study, provide recent examples from a number of applied linguistic domains, and then discuss several important issues, such as gen- eralizability. Although I have written about case study research in applied linguistics in a num- ber of other publications (e.g., Duf & Anderson, 2016; Duf, 2008, 2012a, 2012b, 2014, 2015, 2018, 2019) and have drawn on insights from other case study methodologists (e.g., Merriam, 1998, 2009; Simon, 2009; Stake, 1995, 2006; Yin, 2018), here I provide a recent update on this topic that I hope extends that previous work. Since my own research is primarily concerned with language learning and multilingual socialization across the lifespan, this chapter dis- cusses case study as a method, an approach, or a strategy for examining language learners (speakers, writers, performers) embedded within typically transnational social contexts. Much of my own recent case study research and research supervision concerns heritage-language and Chinese-L2 learning, Generation 1.5 and study-abroad (English-L2) experiences, and