The twentieth century saw dramatic increases in nonmarital births, concentrated heavily among poor and working-class women. In this paper, we investigate whether the oral contraceptive pill played a causal role in the rise of nonmarital births. Exploiting exogenous variation in laws governing access to the pill, we find that changes in marital access to the pill increased the nonmarital birthrate by between 15% and 18%, accounting for about one-third of the overall increase in nonmarital births. These effects are concentrated almost entirely among women whose fathers did not graduate high school and among minority women. We also document that the pill increased spacing between first and second births, and lowered the probability that a woman obtained a high-school diploma, consistent with increases in nonmarital births. We find no evidence that postsecondary education levels were influenced by pill access, and no evidence that nonmarital births move with male employment patterns. Our findings add to a growing literature which documents the power of the pill to shape women's lives in broadly heterogenous ways, with minority and less-well-educated women bearing the brunt of the losses, a phenomenon we call the paradox of the pill. (JEL J12, J13, I24) * We are grateful to the editor and three anonymous referees for improving the manuscript considerably; we also thank