Swearing on the Horns is a farcical oath that was traditionally given to visitors at various pubs in the north London suburb of Highgate during the 17th, 18th and 19th centuries. The oath consists of a series of statements read by a clerk, confirming one's dedication to merriment and debauchery; those being sworn in would agree to each statement, kiss or salute a set of horns, and be entered in a logbook for posterity.

The proceedings were typically overseen by the landlord—referred to as the Master, the Father, or the Host—often dressed in formal costume, such as that of a barrister. In some houses, an "initiation fee" of money or drinks was required in addition to the oath; in others, the fee could be paid to bypass the ceremony altogether. Participants were then awarded the title of "Freemen of Highgate".

The ceremony was a source of amusement for regular customers, who would do their best to convince newcomers to take part in the swearing in. The details of the swearing took various forms across the years and from pub to pub, but maintained the common themes of the horns and many of the individual statements. It seems clear that most participants understood it to be a tourist trap, but were happy to take part in it just the same.