A bailiff is a manager, overseer or custodian – a legal officer to whom some degree of authority or jurisdiction is given. There are different kinds, and their offices and scope of duties vary.

Another official sometimes referred to as a bailiff was the Vogt. In the Holy Roman Empire a similar function was performed by the Amtmann. They are mostly known for being the officer that keeps the order in a court of law and who also administers oaths to people who participate in court proceedings.

Bailiff was the term used by the Normans for what the Saxons had called a reeve: the officer responsible for executing the decisions of a court. The duty of the bailiff would thus include serving summonses and orders, and executing all warrants issued out of the corresponding court. The district within which the bailiff operated was called his bailiwick, and is even to the present day. Bailiffs were outsiders and free men, that is, they were not usually from the bailiwick for which they were responsible.

Throughout Norman England, the Saxon and Norman populations gradually mixed, and reeve came to be limited to shire-level courts (hence sheriff as a contraction of "shire-reeve"), while bailiff was used in relation to the lower courts. Primarily then, bailiff referred to the officer executing the decisions of manorial courts, and the hundred courts. Likewise, in Scotland a bailie was the chief officer of a barony (baron bailie), and in the Channel Islands they were the principal civil officers. With the introduction of justices of the peace (magistrates), magistrates' courts acquired their own bailiffs.

Historically, courts were not only concerned with legal matters, and often decided administrative matters for the area within their jurisdiction. A bailiff of a manor, therefore, would often oversee the manor's lands and buildings, collect its rents, manage its accounts, and run its farms (see Walter of Henley).

In the 19th century, the administrative functions of courts were mostly replaced by the creation of elected local authorities (councils). Nevertheless, the term bailiff is retained as a title by the chief officers of various towns and the keepers of royal castles, such as the High Bailiff of Westminster and the Bailiff of Dover Castle. In Scotland, bailie now refers to a municipal officer corresponding to an English alderman.

In the 20th century, the court system in England was drastically re-organised, with the assize courts taking some of the powers of the shire courts, and becoming the High Court of Justice; in turn, the remaining elements of the shire court took over the powers of the hundred courts, to form county courts. The High Court acquired the sheriffs, the county courts the bailiffs. Bailiffs were now appointed by a county court judge and were removable by the Lord Chancellor.

A bailiff could, for practical reasons, delegate his responsibilities, in regard to some particular court instruction, to other individuals. As the population expanded, the need for the services of a bailiff mainly arose from financial disputes; consequently, these assistants came to be closely associated with debt-collection, in the public's minds. By Shakespeare's time, they had acquired the nickname bum-bailiffs, perhaps because they followed debtors very closely behind them;^{[citation needed]} in France, the term pousse-cul (literally push-arse) was similarly used for their equivalent officers.