Next year will be the 150th anniversary of the “Origin of Species,” in which Darwin established the scientific basis for understanding how evolution occurs by natural selection. Darwin was less clear about the actual process of species formation. Nevertheless, he envisioned a three-step process: colonization, involving the expansion of a population into a new environment; divergence, when populations become adapted to novel environmental conditions through natural selection; and finally, the formation of a barrier to interbreeding between divergent lineages. He showed characteristic insight by suggesting that investigations of what we now call “very young adaptive radiations” might provide windows through which we can view the processes involved. Since Darwin’s time, insights from the fields of genetics, behavior and ecology have continued to illuminate how and why species evolve. In this talk, I will discuss the progress that has been made in our understanding of speciation with special reference to the young radiation of Darwin’s Finches.