This paper explores several paths a distinctive third wave of extended cognition might take. In so doing, I address a couple of shortcomings of first- and second-wave extended cognition associated with a tendency to conceive of the properties of internal and external processes as fixed and non-interchangeable. First, in the domain of cognitive transformation, I argue that a problematic tendency of the complementarity model is that it presupposes that socio-cultural resources augment but do not significantly transform the brain's representational capacities during diachronic development. In this paper I show that there is available a much more dynamical explanation—one taking the processes of the brain's enculturation into patterned practices as transforming the brain's representational capacities. Second, in the domain of cognitive assembly, I argue that another problematic tendency is an individualistic notion of cognitive agency, since it overlooks the active contribution of socio-cultural practices in the assembly process of extended cognitive systems. In contrast to an individualistic notion of cognitive agency, I explore the idea that it is possible to decentralize cognitive agency to include socio-cultural practices.