Livery companies were organizations of master tradesmen which developed in the City of London during the Middle Ages. One of their principal purposes was to control the number and character of new members. Another principal purpose, especially before the Reformation, was social and religious fellowship. Originally the word  “livery” referred to the special clothing of senior members, but later it became associated with distinctive costumes for grand occasions. Prosperous companies in the Middle Ages erected their own livery halls and endowed chapels dedicated to the patron saints of their crafts. Despite the huge changes that have taken place since, several dozen livery companies have survived until the present day. Some of them have in the process become extremely wealthy, and major charitable benefactors. In addition, new livery companies continue to be formed from time to time.

Strictly speaking, a livery company is a company that has received a grant of livery from the City Corporation, i.e. the right to elect “liverymen”. Only liverymen can vote at the annual elections of the Lord Mayor and the Sheriffs, nor can anyone become Lord Mayor who is not first a liveryman of one of the companies. Most livery companies, including those founded in the modern period, will have passed through a stage when they were already accepted as companies (corporate bodies), but had not yet received a grant of livery. Two ancient companies, the Watermen & Lightermen and the Parish Clerks, have never received a grant of livery.

After the formation of the Fan makers in 1709, no new companies were formed for almost 200 years until the Master Mariners in 1926 (livery in 1932). There have been several since. Post-1709 companies are called modern livery companies. Formed in 1999, the Company of Security Professionals became the 108th Livery Company on 19th February 2008.

Ordinary members of livery companies are known as freemen. They become freemen (the technical phrase is “are admitted to the freedom”) by one of three means: apprenticeship to a member of the company, normally for seven years; patrimony, i.e. by right of legitimate birth after one’s father is already a member of the company; and purchase, known as “redemption”. Freemen of a company were then eligible to take up the totally separate freedom of the City of London, which in turn qualifies them for election to the company’s livery, or body of senior members. After that, liverymen can hope to be elected to the Court (governing body) of the company, and eventually to become Master of the company, normally for one year.

In the past, livery companies were responsible for the regulation of their trades, controlling, for instance, wages and labour conditions. Some livery companies such as the Goldsmiths continue to have a regulatory role today, while others have become inoperative except as social and charitable bodies. Those formed in recent years are usually both trade and charitable organizations.

Around forty companies still have a hall, where members and their guests can be entertained and company business transacted. The Merchant Taylors and Goldsmiths are among the earliest companies known to have possessed halls, as far back as the 14th century, and the Merchant Taylors have continued to occupy the same site in Threadneedle Street to the present day. Fragments of the medieval hall are still visible, incorporated into later fabric. Companies that do not have their own hall usually borrow another company's premises for social occasions.