Odd Fellows (or Oddfellows when referencing the Grand United Order of Oddfellows or some British-based fraternities; also Odd Fellowship or Oddfellowship) is an international fraternity consisting of lodges first documented in 1730 in London. The first known lodge was called Loyal Aristarcus Lodge No. 9, suggesting there were earlier ones in the 18th century. Notwithstanding, convivial meetings were held "in much revelry and, often as not, the calling of the Watch to restore order." Names of several British pubs today suggest past Odd Fellows affiliations. In the mid-18th century, following the Jacobite risings, the fraternity split into the rivaling Order of Patriotic Oddfellows in southern England, favouring William III of England, and the Ancient Order of Oddfellows in northern England and Scotland, favouring the House of Stuart.

Odd Fellows from that time include John Wilkes (1725–1797) and Sir George Savile, 8th Baronet of Thornton (1726–1784), advocating civil liberties and reliefs, including Catholic emancipation. Political repressions, such as the Unlawful Oaths Act (1797) and the Unlawful Societies Act (1799), resulted in neutral amalgamation of the Grand United Order of Oddfellows in 1798. Since then, the fraternity has remained religiously and politically independent. George IV of the United Kingdom, admitted in 1780 while he was Prince of Wales, was the first documented of many Odd Fellows to also attend freemasonry, although the societies remain mutually independent.^{[citation needed]}

In 1810, further instigations led to the establishment of the Independent Order of Oddfellows Manchester Unity in England. Odd Fellows spread overseas, including formally chartering the fraternity in the United States in 1819. In 1842, due to British authorities intervening in the customs and ceremonies of British Odd Fellows and in light of post-colonial American sovereignty, the American Odd Fellows became independent as the Independent Order of Odd Fellows (always written as Odd Fellows, not Oddfellows like other orders) under British-American Thomas Wildey (1782–1861), soon constituting the largest sovereign grand lodge. The Daughters of Rebekah, now known as the International Association of Rebekah Assemblies, was established in 1851 as a women's auxiliary organization to the Independent Order of Odd Fellows. Likewise, by the mid-19th century, the Independent Order of Oddfellows Manchester Unity had become the largest and richest fraternal organisation in the United Kingdom.^{[failed verification]}

In 1843, rejected from the Independent Order of Odd Fellows due to race, Peter Ogden petitioned the Grand United Order of Oddfellows for a charter and was granted it forming the Philomathean Lodge, No. 646, in New York City. The women's auxiliary organization, Household of Ruth, was established in 1858.

Odd Fellows promote philanthropy, the ethic of reciprocity and charity; some grand lodges imply a Judeo-Christian affiliation. The American-based Independent Order of Odd Fellows enrolls some 600,000 members divided into approximately 10,000 lodges in thirty countries, and is interfraternally recognised by the British-based Independent Order of Oddfellows Manchester Unity. In total, members of all international branches combined are estimated in the millions worldwide.^{[citation needed]}

Several theories aim to explain the etymological background of the name "Odd Fellows," often rendered "Oddfellows" in British English. In 18th-century United Kingdom, major trades were organised in guilds or other forms of syndicates, but smaller trades did not have equivalent social or financial security. One theory has it that "odd fellows", people who exercised unusual, miscellaneous "odd trades", eventually joined together to form a larger group of "odd fellows."

Another theory suggests that in the beginning of odd fellowship in the 18th century, at the time of the early era of industrialisation, it was rather odd to find people who followed noble values such as fraternalism, benevolence, and charity.^{[need quotation to verify]} The name was supposedly adopted at a time when the severance into sects and classes was so wide that persons aiming at social union and mutual help were a marked exception to the general rule. Possibly, it met a mixed reaction from the upper classes, who may have seen them as a source of revenue by taxes, but also as a threat to their authority.

Any suggestion of history before the 18th century is considered mere speculation.