Changes in the timing and level at which genes are expressed are known to play an important role in evolution, but the mechanisms underlying changes in gene expression remain relatively obscure. Until quite recently, evolutionary biologists, like most biologists, tended to study single genes as isolated entities. These studies have added enormously to our understanding of biological evolution. But because gene regulation by its very nature involves interactions between two (or more) genes, researchers have missed a range of evolutionary phenomena that can be observed only at the level of networks of interacting genes. In this article, we consider the change in perspective that genomic technologies—particularly the advent of large-scale platforms for DNA sequencing, genotyping, and measuring gene expression—are bringing to evolutionary biology. We focus specifically on how these technologies can and are being used to increase our understanding of how and why gene expression evolves.