Through conceptual and empirical means, this timely volume looks at how critical realism, a specific approach to the philosophy of science, helps uncover and refine assumptions about what constitutes valid knowledge in applied linguistics, how scholars can create it, and how applied linguistics can improve as an interdisciplinary strand of the social sciences. With contributions from leading and up-and-coming scholars in the field, the book covers a range of topics, from language, language learning and teaching, language curriculum and programmes, evaluation and assessment, academic writing, discourse, beliefs, values, truth, resilience, ethnicity, social class, as well as ideologies and systems of social inequality including anthropocentrism, racism, linguicism, sexism, patriarchy, and neoliberalism. Exploring the philosophical basis of applied linguistics research, it is essential reading for academic scholars and graduate students in applied linguistics, as well as social scientists interested in language-related issues and social issues in which language plays a central role.