This article revisits complex dynamic systems theory (CDST) and provides a new synthesis that, the authors argue, may empower language teachers. The particular focus is on the interplay between change and stability in complex dynamic systems, including language teaching and learning. The article identifies four key dynamical properties of complex dynamic systems, which reflect change, stability, and the interplay between these two. The dynamical properties are historicity, adaptiveness, nonlinearity, and emergence. The authors associate these dynamic properties with four recognisable types of activity: normative, contingent, creative, and purposeful teaching and learning. The central argument is that language teaching and learning are interconnected, and language teaching that promotes these four types of teaching and learning activity may also promote opportunities for language learning. The authors conclude with a discussion of how teachers may use this CDST perspective to reflect on three aspects of their professional context--teaching, language, and agency--and how such reflection, followed by action, may promote opportunities for language learning in their contexts.