Connecting deeply with another mind is as enigmatic as it is fulfilling. Why people “click” with some people but not others is one of the great unsolved mysteries of science. However, researchers from psychology and neuroscience are converging on a likely physiological basis for connection – neural synchrony (entrainment). Here, we review research on the necessary precursors for interpersonal synchrony: the ability to detect a mind and resonate with its outputs. Further, We describe potential mechanisms for the development of synchrony between two minds. We then consider recent neuroimaging and behavioral evidence for the adaptive benefits of synchrony, including neural efficiency and the release of a reward signal that promotes future social interaction. In nature, neural synchrony yields behavioral synchrony. Humans use behavioral synchrony to promote neural synchrony, and thus, social bonding. This reverse-engineering of social connection is an important innovation likely underlying this distinctively human capacity to create large-scale social coordination and cohesion.