Do you know who George Williams is? If you don't, let me introduce you to one of the most influential evolutionary biologists ever to ponder natural selection. If you do know who he is, you may still be interested in my article in this week's Science about a symposium that was recently held in Williams's honor. Scientists studying everything from pregnancy to economic decision making explained how Williams's remarkably clear thinking about the nature of adaptation helped them in their research. A pdf of the article is also available.