Agency has attracted considerable attention, especially of late. Nevertheless, perceptions of language learners as nonagentive persist. In this article the Douglas Fir Group's call for a transdisciplinary perspective is heeded in a Complex Dynamic Systems Theory's (CDST) conceptualization of agency. It is suggested that CDST maintains the structure-agency complementarity while bringing to the fore the relational and emergent nature of agency. Coordination dynamics is identified as a possible mechanism for the phylogenetic and ontogenetic emergence of agency. CDST further characterizes agency as spatially-temporally situated. It can be achieved and changed through iteration and co-adaptation. It is also multidimensional and heterarchical. In this era of posthumanism, an issue that is also taken up is whether it is only humans who have agency. The article then discusses educational practices that could support learner agency. Finally, the article closes with a discussion of agency and ethical action.