 The popularity of the emergentist vision waned beginning shortly after Broad’s writing, with important scientific developments eroding the boundaries between adjacent “levels” (most notably quantum chemistry and molecular biochemistry—see McLaughlin 1992 for discussion). However, attention to emergence was substantially reinvigorated starting in the 1970s with the discovery and creation of non-linear complex systems of both natural and artifactual varieties. There is now a large recent literature developing accounts of emergence motivated by such systems. It has gradually broadened to encompass mental phenomena that seem to resist physicalist treatment (e.g., consciousness and free will) and some have even begun to re-think received wisdom concerning the relationship of chemistry and biology to lower-level sciences. These debates are of considerable importance for our understanding of the natural world and of our own place within it. As the bibliography attests, the questions at issue here engage philosophers and scientists alike. This should be unsurprisingly, for these questions are neither simply empirical nor wholly a priori in character, but are rather such that plausible (if not uncontroversial) answers require consideration of and support for metaphysical interpretations of the structure of natural reality in light of our best empirical theories.