Mother's Day is a celebration honoring the mother of the family or individual, as well as motherhood, maternal bonds, and the influence of mothers in society. It is celebrated on different days in many parts of the world, most commonly in March or May. It complements similar celebrations, largely pushed by commercial interests, honoring family members, such as Father's Day, Siblings Day, and Grandparents' Day.

While some countries have a multi-century history of a day to celebrate mothers, the modern American version of the holiday began in the United States in the early 20th century at the initiative of Anna Jarvis. She organized the first Mother's Day service of worship and celebration at Andrews Methodist Episcopal Church in Grafton, West Virginia, which serves as the International Mother's Day Shrine today. It is not directly related to the many traditional celebrations of mothers and motherhood that have existed throughout the world over thousands of years, such as the Greek cult to Cybele, the mother deity Rhea, the Roman festival of Hilaria, or the other Christian ecclesiastical Mothering Sunday celebration (associated with the image of Mother Church). However, in some countries, Mother's Day is still synonymous with these older traditions.

The American version of Mother's Day has been criticized for having become too commercialized. Jarvis herself, who began the celebration as a liturgical observance, regretted this commercialism and expressed that this was never her intention. In response, Constance Adelaide Smith successfully advocated for Mothering Sunday, commemorating a broader definition of motherhood in many other parts of the English-speaking world.

The modern holiday was first celebrated in 1907 when Anna Jarvis held the first Mother's Day worship service at Andrews Methodist Episcopal Church in Grafton, West Virginia. Andrew's Methodist Church now holds the International Mother's Day Shrine. Her campaign to make Mother's Day a recognized holiday in the United States began in 1905, when her mother, Ann Reeves Jarvis, died. Ann Jarvis had been a peace activist who cared for wounded soldiers on both sides of the American Civil War and created Mother's Day Work Clubs to address public health issues. She and another peace activist and suffragette, Julia Ward Howe, had been urging to create a "Mother's Day For Peace" where mothers would ask that their husbands and sons were no longer killed in wars. 40 years before it became an official holiday, Ward Howe had made her Mother's Day Proclamation in 1870, which called upon mothers of all nationalities to band together to promote the "amicable settlement of international questions, the great and general interests of peace." Anna Jarvis wanted to honor this and to set aside a day to honor all mothers because she believed a mother is "the person who has done more for you than anyone in the world."

In 1908, the U.S. Congress rejected a proposal to make Mother's Day an official holiday, joking that they would also have to proclaim a "Mother-in-law's Day." However, owing to the efforts of Anna Jarvis, by 1911, all U.S. states observed the holiday, with some of them officially recognizing Mother's Day as a local holiday (the first being West Virginia, Jarvis' home state, in 1910). In 1914, Woodrow Wilson signed a proclamation designating Mother's Day, held on the second Sunday in May, as a national holiday to honor mothers.

Although Jarvis, who started Mother's Day as a liturgical service, successfully founded the celebration, she became resentful of the commercialization of the holiday. By the early 1920s, Hallmark Cards and other companies had started selling Mother's Day cards. Jarvis believed that the companies had misinterpreted and exploited the idea of Mother's Day and that the holiday's emphasis was on sentiment, not profit. As a result, she organized boycotts for Mother's Day and threatened to issue lawsuits against the companies involved. Jarvis argued that people should appreciate and honor their mothers through handwritten letters expressing their love and gratitude instead of buying gifts and pre-made cards. Jarvis protested at a candy makers' convention in Philadelphia in 1923 and a meeting of American War Mothers in 1925. By this time, carnations had become associated with Mother's Day, and the selling of carnations by the American War Mothers to raise money angered Jarvis. He was arrested for disturbing the peace.

In Britain, Constance Adelaide Smith was inspired to advocate for Mothering Sunday, an already-existing Christian ecclesiastical celebration in which the faithful visit the church where they received the sacrament of baptism, as an equivalent celebration. She referred to medieval traditions of celebrating Mother Church, 'mothers of earthly homes,' Mary, mother of Jesus, and Mother Nature. Her efforts were successful in the British Isles and other parts of the English-speaking world.

The United States celebrates Mother's Day on the second Sunday in May. In 1872 Julia Ward Howe called for women to join in support of disarmament and asked for 2 June 1872 to be established as a "Mother's Day for Peace." Her 1870 "Appeal to womanhood throughout the world" is sometimes referred to as Mother's Day Proclamation. But Howe's day was not for honoring mothers but for organizing pacifist mothers against war. In the 1880s and 1890s, there were several further attempts to establish an American "Mother's Day," but these did not succeed beyond the local level.

In the United States, Mother's Day remains one of the biggest days for selling flowers, greeting cards, and the like; Mother's Day is also the biggest holiday for long-distance telephone calls. Moreover, churchgoing is also popular on Mother's Day, yielding the highest attendance after Christmas Eve and Easter. Many worshippers celebrate the day with carnations, colored if the mother is living and white if she is dead.

Mother's Day continues to be one of the most commercially successful U.S. occasions.

It is possible that the holiday would have withered over time without the support and continuous promotion of the florist industries and other commercial industries. Other Protestant holidays from the same time, such as Children's Day and Temperance Sunday, do not have the same level of popularity.