On the extended mind hypothesis (EM), many of our cognitive states and
processes are hybrids, unevenly distributed across biological and nonbiological realms. In certain circumstances, things - artifacts, media, or technologies - can have a cognitive life, with histories often as idiosyncratic as those of the embodied brains with which they couple. The realm of the mental can spread across the physical, social, and cultural environments as well as bodies and brains. My independent aims in this chapter are: first, to describe two compatible but distinct movements or "waves" within the EM literature, arguing for the priority of the second wave (and gesturing briefly toward a third); and, second, to defend and illustrate the interdisciplinary implications of EM as best understood, specifically for historical disciplines, by sketching two case studies.