The Woman's Christian Temperance Union (WCTU) is an international temperance organization. It was among the first organizations of women devoted to social reform with a program that "linked the religious and the secular through concerted and far-reaching reform strategies based on applied Christianity." It plays an influential role in the temperance movement. Originating among women in the United States Prohibition movement, the organization supported the Eighteenth Amendment and was also influential in social reform issues that came to prominence in the Progressive Era.

The WCTU was originally organized on December 23, 1873, in Hillsboro, Ohio, and, starting on December 26, Matilda Gilruth Carpenter led a successful campaign to close saloons in Washington Court House, Ohio. WCTU was officially declared at a national convention in Cleveland, Ohio, November 18–20, 1874.

It operated at an international level and in the context of religion and reform, including missionary work and women's suffrage. Two years after its founding, the American WCTU sponsored an international conference at which the International Women's Christian Temperance Union was formed. The World's Woman's Christian Temperance Union was founded in 1883 and became the international arm of the organization, which now has affiliates in Australia, Canada, Netherlands, Finland, India, Japan, New Zealand, Norway, South Korea, United Kingdom, and the United States, among others.

The Woman's Christian Temperance Union conducts a White Ribbon Recruit (WRR) ceremony, in which babies are dedicated to the cause of temperance through a white ribbon being tied to their wrists, with their adult sponsors pledging to help the child live a life free from alcohol and other drugs.

At its founding in 1874, the stated purpose of the WCTU was to create a "sober and pure world" by abstinence, purity, and evangelical Christianity. Annie Wittenmyer was its first president. Wittenmyer was conservative in her goals for the movement focusing only on the question of alcohol consumption and avoiding involvement in politics. The constitution of the WCTU called for "the entire prohibition of the manufacture and sale of intoxicating liquors as a beverage."

Frances Willard, the second WCTU president, objected to this limited focus of social issues WCTU was addressing. Willard believed that it was necessary for the WCTU to be political in women's issues for the success, expansion, and implementation of the WCTU. From 1879, Willard was the president of the WCTU until her death in 1898. During her presidency, the WCTU grew significantly and established the relationship between temperance and suffrage. Despite advocating for women, WCTU did not challenge gender roles, rather they integrated elements of "protofeminism" into the organization.

Its members were inspired by the Greek writer Xenophon, who defined temperance as "moderation in all things healthful; total abstinence from all things harmful." In other words, should something be good, it should not be indulged in to excess; should something be bad for you, it should be avoided altogether—thus their attempts to rid society of what they saw (and still see) as the dangers of alcohol.

The WCTU perceived alcohol as a cause and consequence of larger social problems rather than as a personal weakness or failing. The WCTU also advocated against tobacco. The American WCTU formed a "Department for the Overthrow of the Tobacco Habit" as early as 1885 and frequently published anti-tobacco articles in the 1880s. Agitation against tobacco continued through to the 1950s.