Our understanding of admixture between humans and Neanderthals has changed dramatically over the past decade and a half. Once thought not to have occurred at all, there is now ample evidence for gene flow from Neanderthals to humans and vice versa. Li et al. used a new framework to model the increasingly complex dynamics of introgression between humans and Neanderthals and the ramifications for both populations. They identified regions of human ancestry in Neanderthals, estimated population sizes for Neanderthals were about 20% lower than previously thought, and proposed the possibility of two pulses of gene flow from humans to Neanderthals.