The One-Child Policy is often perceived as a government-mandated quota system. Recent research acknowledges regional incentives allowing women to have more than one child. The policy was actually an individually tailored pricing system varying within each woman's life cycle. I document and exploit this variation to nd that the policy: only affected women whose first child was a girl; did (not) reduce the number of girls (boys) born per woman; and caused a minor decrease in aggregate fertility. Data on ultrasound availability suggest that the second finding, but not the first, results at least partly from prenatal sex selection.