Margaret Sanger devoted her life to make birth control legal and universally available. She established the first birth control clinic in 1916 in New York and from the mid-1920s onwards, „Sanger clinics“ spread over the entire US. Combining data on the role out of these clinics, census data and vitality statistics, this paper is the first attempt to assess the causal impact of these clinics on fertility and other socio-economic outcomes. Our results suggest that women who had been exposed 25 years, i.e. between the age of 15 and 39 to a birth control clinic in their own or an adjacent county would have experienced a fertility level 10 to 15% lower compared to women without any exposure. In larger cities this effect even increases to 20 to 25%. Moreover, we find that birth control clinics reduced child mortality by about 5% and all-age mortality by about 3%, probably entirely driven by lower female mortality. We also find positive effects on female labor supply and female employment, yet these effects are probably dampened by the Great Depression. Overall, we interpret these findings as the consequence of a supply side policy that relaxed constraints on the demand side. Although at the margin the offered information and services may also have changed preferences over children, this was not the aim of these clinics and there is little evidence that this has been the key mechanism as at the time of their establishment the fertility transition was already well under way. These results provide new evidence on the driving forces of the demographic transition in the US.