Freemasonry is a fraternal organisation that arose from obscure origins in the late 16th to early 17th century. Freemasonry now exists in various forms all over the world, with a membership estimated at around 5 million (including around 480,000 in England, Scotland and Ireland alone, and just under two million in the United States).

A fraternity is a brotherhood, though the term usually connotes a distinct or formal organization. The only true distinction between a fraternity and any other form of social organization is the implication that the members freely associate as equals for a mutually beneficial purpose, rather than because of a religious, governmental, commercial, or familial bond.

There are known fraternal organizations which existed as far back as ancient Greece and Rome and analogous institutions, called confraternities, which existed, allied to the Catholic Church, in the late medieval period.

The development of Freemasonry in the early 1700s became a watershed moment in fraternal organization, and there have been hundreds of varieties of Freemasonry, and thousands of closely parallel organizations since then. Virtually all fraternal organizations today bear some debt to the models of organization first worked out in Masonic lodges.

The development was especially dynamic in the United States, where the freedom to associate outside governmental regulation is expressly sanctioned in law. There have been hundreds of fraternal organizations in the United States, and at the turn of the last century the number of memberships was equal to the number of adult males, although, because of multiple memberships, probably only 50% of adult males belonged to any organizations.

Freemasonry uses the metaphors of operative stonemasons' tools and implements, against the allegorical backdrop of the building of King Solomon's Temple, to convey what has been described by both Masons and critics as "a system of morality veiled in allegory and illustrated by symbols."

The origins and early development of Freemasonry are a matter of some debate and conjecture. There is some evidence to suggest that there were Masonic Lodges in existence in Scotland as early as the late sixteenth century, and clear references to their existence in England by the mid seventeenth century. A poem known as "The Regius Manuscript" has been dated to approximately 1390 and is the oldest known Masonic text.

The first Grand Lodge, the Grand Lodge of England (GLE), was founded on 24 June 1717, when four existing London Lodges met for a joint dinner. This rapidly expanded into a regulatory body, which most English Lodges joined. However, a few lodges resented some of the modernisations that GLE endorsed, such as the creation of the Third Degree, and formed a rival Grand Lodge on 17 July 1751, which they called the "Antient Grand Lodge of England". The two competing Grand Lodges vied for supremacy—the "Moderns" (GLE) and the "Antients" (or "Ancients")—until they united 25 November 1813 to form the United Grand Lodge of England (UGLE).

The Grand Lodges of Ireland and Scotland were formed in 1725 and 1736 respectively. Freemasonry was exported to the British Colonies in North America by the 1730s—with both the "Antients" and the "Moderns" (as well as the Grand Lodges of Ireland and Scotland) chartering offspring ("daughter") Lodges, and organising various Provincial Grand Lodges. After the American Revolution, independent U.S. Grand Lodges formed themselves within each State. Some thought was briefly given to organising an over-arching "Grand Lodge of the United States", with George Washington (who was a member of a Virginian lodge) as the first Grand Master, but the idea was short-lived. The various State Grand Lodges did not wish to diminish their own authority by agreeing to such a body.

Although there are no real differences in the Freemasonry practiced by lodges chartered by the Antients or the Moderns, the remnants of this division can still be seen in the names of most Lodges, F.& A.M. being Free and Accepted Masons and A.F.& A.M. being Antient Free and Accepted Masons.