There are 110 livery companies, comprising London's ancient and modern trade associations and guilds, almost all of which are styled the 'Worshipful Company of' their respective craft, trade or profession. These livery companies play a significant part in the life of the City of London (i.e. the financial district and historic heart of the capital), not least by providing charitable-giving and networking opportunities. Liverymen retain voting rights for the senior civic offices, such as the Lord Mayor, Sheriffs and Corporation, its ancient municipal authority with extensive local government powers.

The term livery originated in the specific form of dress worn by retainers of a nobleman and then by extension to special dress to denote status of belonging to a trade. Livery companies evolved from London's medieval guilds, becoming corporations under royal charter responsible for training in their respective trades, as well as for the regulation of aspects such as wage control, labour conditions and industry standards. Early guilds often grew out of parish fraternal organizations, where large groups of members of the same trade lived in close proximity and gathered at the same church. Like most organisations during the Middle Ages, these livery companies had close ties with the Catholic Church (before the Protestant Reformation), endowing religious establishments such as chantry chapels and churches, observing religious festivals with hosting ceremonies and well-known mystery plays. Most livery companies retain their historical religious associations, although nowadays members are free to follow any faith or none. Companies often established a guild or meeting hall, and though they faced destruction in the Great London Fire of 1666 and during the Blitz of World War II, around forty companies still own or share ownership of halls, some elaborate and historic, others modern replacements for halls destroyed or redeveloped. Most of these halls are made available for use by other companies not having a hall of their own.

Most ancient livery companies maintain contact with their original trade or craft. In some cases, livery companies have chosen to support a replacement industry fulfilling a similar purpose today, e.g. plastics replacing use of horn or ivory. Modern companies are mainly represented by today's professions and industry and operate in close association with these. Many ancient crafts remain as relevant today as when their guilds were originally established. Some still exercise powers of regulation, inspection and enforcement, while others are awarding bodies for professional qualifications. The Scriveners' Company admits senior members of legal and associated professions, the Apothecaries' Society awards post-graduate qualifications in some medical specialities, and the Hackney Carriage Drivers' Company comprises licensed taxi drivers who have passed the "Knowledge of London" test. Several companies restrict membership to those holding relevant professional qualifications, e.g. the City of London Solicitors' Company and the Worshipful Company of Engineers. Other companies whose trade died out long ago, such as the Longbow Makers' Company, have evolved into being primarily charitable foundations. Some companies disappeared entirely such as Pinmakers.

After the Worshipful Company of Carmen received City livery status in 1848 no new companies were established for 80 years until the Honourable Company of Master Mariners in 1926 (granted livery in 1932). Post-1926 creations are known as modern livery companies. The Worshipful Company of Arts Scholars, the newest, was granted livery status on 11 February 2014, making it the 110th City livery company in order of precedence. The Honourable Company of Air Pilots is exceptional among London's livery companies in having active overseas committees in Australia, Canada, Hong Kong, New Zealand and North America.