This dissertation explores the nearly simultaneous acceptance of contraceptives among Protestants in Britain and the United States in the early twentieth century. In August of 1930, the Lambeth Conference of Anglican bishops officially approved contraceptives in Britain. Only months later, in March of 1931, the Federal Council of Churches in the United States did the same. Because this was the first time two significant bodies of Protestants had incorporated contraceptive use into their official Christian teaching, they provide an informative window into how and why contraceptives were accepted within the English speaking world.Part One examines how the Lambeth Conference of 1930 both offered public sanction to contraception and rejected the Anglicans' historical reliance on self-control as a superior method of family planning. It finds that in the late-nineteenth and early-twentieth century, the Anglican leadership drew on a widely shared culture of self-control to conclude that contraceptives had no place in a normal, healthy marriage. The leadership did, however, generally agree that regulating births was desirable in some cases. For such regulation, Anglican leaders consistently proposed periodic sexual abstinence. In the 1920s, pressure for contraceptive acceptance became increasingly public as contraceptive advocates openly questioned the feasibility of sexual self-restraint within marriage. By the Lambeth Conference of 1930 an intense controversy had emerged, in which advocates for contraception pressed their case: self-restraint within marriage was untenable and unnatural; contraceptives could be a regular part of a healthy marriage. In a dramatic reversal of previous guidance, the Conference declared that there was, after all, moral space for contraceptives within Christian marriage.Part Two examines how in the U.S the Federal Council of Churches came to a similar acceptance and identifies a parallel historical development. From the late nineteenth century through the first decade of the twentieth century, a strong social purity culture dominated by evangelical Protestants depended upon, educated for, and legally reinforced the plausibility of sexual self-control as a method for regulating births. In the 1920s, proponents of contraception vigorously and publicly challenged the plausibility of sexual self-control within marriage. Initially, in 1929, Council leaders responded to this challenge, which they called the "marriage crisis," with the traditional language of self-control. But in 1931, the Council issued a statement accepting contraceptives. At its heart was a desire to assist the wider social acceptance of contraceptives and a deep doubt about the plausibility of sexual abstinence within marriage. In sum, this study contends that in order to understand Protestant acceptance of contraceptives, one also needs to understand the declining acceptance of previous arguments for sexual abstinence.In making this argument, this dissertation considers an array of contextual factors, like medical developments, class consciousness, public advocacy, demographic factors, and theological change. Beyond Protestantism, there is a pertinent comparison with an encyclical from Pope Pius XI, Casti Connubii, of December 1930, that upheld the Catholic prohibition on contraception.