This study examines how language teachers develop metacognitive thought and action in their practice. Using the conceptual framework of complexity theory to frame language teacher metacognition as a multidimensional, adaptive, and emergent outcome, the aim of this study is to investigate whether and how teacher metacognition contributes to successful language teaching practice. Using critical case sampling, data were collected from 40 Korean English-language teachers in public school (i.e., K-12) settings. This dataset included (a) reflective journal entries (four times per teacher over 12 months), (b) observational data (two regular lessons at different time points in the year for each teacher), and (c) verbal commentary interview on these observed classes and journals. Our analysis examines what language teacher metacognition entails, how it develops and is maintained, and how it impacts teachers' practice in the ecology of the L2 classroom. Our findings suggest that awareness of phenomenological aspects of teachers' classroom persona and instructional practices-what we term "inside-out thinking"-shape language teachers' metacognition through their intentionality for making a difference in their students' development. We discuss how exploring the tensions between language teachers' metacognition and their classroom practice can help address the link between language teachers' inner lives and their teaching.