The YMCA was founded in London, England on June 6, 1844 by Sir George Williams in response to unhealthy social conditions arising in London at the end of the Industrial Revolution. Since then the YMCA has grown to become a world-wide movement of more than 45 million members from 124 national federations affiliated through the World Alliance of YMCAs.

In 1844, the concept of a YMCA, which began among evangelicals, was unusual because it crossed the rigid lines that separated the different churches and social classes of England, making the YMCA a pioneer of ecumenism. This openness was a trait that would eventually lead to the inclusion of women and children, and a culture of acceptance of people of different faiths and backgrounds. Today the degree to which religion is emphasized in programs varies between individual YMCA associations. Generally, YMCAs are open to all, regardless of faith, social class, age, or gender.

Its name represents something of an anachronism, but it has been retained as a strong brand name.

Organization
The YMCA is organized as a federation of local associations and national YMCA movements. Within most countries, the local YMCAs are related primarily in terms of overall strategy and direction only. Volunteers and local employees operate the individual YMCA associations.

The federated model of governance has created a diversity of YMCA programs and services, with YMCAs in different countries and communities offering vastly different programming in response to local community needs. In North America, the YMCA is sometimes perceived to be primarily a community sports facility; however it offers a broad range of programs such as sports, personal fitness, child care, overnight camping, employment readiness programs, conference centers and educational activities as methods of promoting positive values.

Mission
Although local variations in mission exist and the YMCA's collectively expressed mission has evolved since its founding, the international YMCA movement's mission historically has been one of promoting Ecumenical Christianity.

Activities
The activities of the YMCA work to build healthy mind, body and spirit for all, and there are many activities that work to achieve these goals.

Healthy spirit
The first YMCA was concerned with Bible study, although the organization has generally moved on to a more holistic approach to youth work. Around six years after its birth, an international YMCA conference in Paris decided that the objective of the organization should become "Christian discipleship developed through a program of religious, educational, social and physical activities" (Binfield 1973:265). More recent objectives as found on the YMCA UK website include no reference to discipleship.

Healthy mind
Many colleges and universities owe their creation to the YMCA. Springfield College was founded in 1885 as an international training school for YMCA Professionals, while Sir George Williams University—one of the two schools that eventually became Concordia University—started from night courses offered at the Montreal YMCA.

Northeastern University (Boston, Massachusetts) began out of a YMCA in Boston, and Franklin University began as the YMCA School of Commerce.

The YMCA pioneered the concept of night school, providing educational opportunities for people with full-time employment. Many YMCAs offer ESL programs, alternative high school, day care, and summer camp programs.

American high school students have a chance to participate in YMCA Youth and Government, wherein clubs of kids representing each YMCA community convene annually in their respective state legislatures to "take over the State Capitol for a day." YMCA Youth and Government helps teens learn about and participate in civics in a real-world setting.

Healthy body
In 1891 James Naismith, a Canadian, invented basketball whilst studying at the YMCA International Training School in Springfield, Massachusetts (later to be named Springfield College). Naismith had been asked to invent a new game in a desperate attempt to interest pupils in physical exercise. The game had to be interesting, easy to learn, and easy to play indoors in winter. Such an activity was needed both by the Training School and by YMCAs across the country. It was a success from the very first game.

Naismith and his wife attended the 1936 Summer Olympics when basketball became one of the Olympic events.

In 1895, William G. Morgan from the YMCA of Holyoke, Massachusetts invented the sport of volleyball.

Residences
Until the late 1950s, YMCAs in the United States were built with hotel-like rooms called residences or dormitories. These rooms became a significant part of American culture, known as an inexpensive and safe place for a visitor to stay in an unfamiliar city. In 1940 there were about 100,000 rooms at YMCAs, more than any hotel chain. By 2006, YMCAs with residences became relatively rare in the US but many still existed.

Many YMCAs throughout the world still maintain residences as an integral part of the programming.