What constitutes a "good teacher" and "good teaching" has come under much scrutiny in an age of globalization, transnationalism, and increased demands for accountability. It is against this evolving landscape and the pathbreaking work of the Douglas Fir Group (DFG, 2016) that this special issue engages the following two broad questions: (a) In what ways is language teaching "identity work?" and (b) To what extent does a transdisciplinary approach to language learning and teaching offer insight into language teacher identity? We begin this Introduction with a discussion on identity research in second language acquisition and applied linguistics, and then address innovations in language teacher identity research, exploring how this work has been advanced methodologically through narratives, discourse analysis, and an ethical consideration of research practices. We then consider how the transdisciplinary framework of the DFG, and its focus on macro, meso, and micro dimensions of language learning at the ideological, institutional, and classroom levels, respectively, might contribute to our understanding of language teacher identity. In the final section, we argue that the host of complementary theories adopted by the six contributors supports the view that a transdisciplinary approach to language teacher identity is both productive and desirable. Further, the contributors advance the language teacher identity research agenda by taking into consideration (a) how teacher identity intersects with the multilingual (Higgins and Ponte) and translingual (Zheng) realities of contemporary classrooms, (b) the investment of teachers in developing the semiotic repertoires of learners (Stranger-Johannessen and Norton) and a socially inclusive learning environment (Barkhuizen), and (c) the emotions (Wolff and De Costa) and ethical practices (Miller, Morgan, and Medina) of teachers. Central to all articles in this special issue is the need to recognize the rich linguistic and personal histories that language teachers bring into the classroom in order to promote effective language learning.