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A Master is judicial officer found in the courts of England and in numerous other jurisdictions based on the common law tradition. A master's jurisdiction is generally confined to civil proceedings and is a subset of that of a judge. Masters are typically involved in hearing motions, case management, dispute resolution or adjudication of specific issues referred by judges. Their functions would otherwise fall to the judges of the court.
Besides the courts of England & Wales, masters may be found in the Republic of Ireland, Australia, New Zealand, several Caribbean countries and a number of Canadian provinces. Several state courts in the United States utilize masters or similar officers and also make extensive use of special masters.
United Kingdom 
The role of a Master in the High Court of Justice of England and Wales is concerned primarily with procedural matters such as applications, motions and case management. There are masters in both the Queen's Bench and Chancery Divisions and their roles differ slightly.
Such a person is known professionally as, for example, "Master Smith". This is so whether the Master is male or female. A similar type of Master exists in the Court system of Northern Ireland, in several Canadian and Australian jurisdictions as well as in other countries whose court system is based on that of England.
The office of Master is of ancient origins dating from at least the 12th century. Originally part of the mechanism of the court of Chancery, masters were retained and their functions merged with similar officers in the common law courts when courts of law and equity were fused in the late 19th century. There are masters in the Chancery and Queen's Bench divisions of the High Court of Justice. The Senior Master of the Queen's Bench Division also bears the title of Queen's Remembrancer which is one of the oldest judicial offices in England.
In the Inns of Court, the members of the governing body are known as "Masters of the Bench" or, more commonly, "benchers". In the context of the functions they perform in that capacity (but not otherwise) they will be known as, for example, "Master Smith" (whether they are male or female). This will be so even if in other contexts they use a higher title: hence, a High Court Judge who is a Master of the Bench will be known in his or her Inn as "Master Smith", in private life as Sir John Smith, and on the bench as Mr Justice Smith; likewise a law lord will be known in the inn as "Master Woolf" even if he is privately and professionally known by the peerage title of "Lord Woolf".
Republic of Ireland 
The judicial system of the Republic of Ireland has a judicial official termed “Master of the High Court". The Master is authorised by law to exercise limited functions and powers of a judicial nature within the scope of Article 37 of the Constitution of Ireland. He/she may not exercise any function in several areas including criminal proceedings, the granting of injunctions, bail, custody of children and matters concerning wards of court. Though the office of Master of the High court is very old, its powers and functions were redefined by the Courts and Court Officers Act, 1995.
In Canada the structure of the court system is primarily a provincial responsibility and the superior courts of the provinces have different names. Masters are found in the Supreme Court of British Columbia, Court of Queen's Bench of Alberta, the Court of Queen's Bench of Manitoba and the Ontario Superior Court of Justice. There are part time taxing masters in the Supreme Court of Newfoundland and Labrador. There is a similar office of prothonotary in the Supreme Court of Prince Edward Island and in the Federal Court.
The jurisdiction of a Master is fixed by provincial statute and the rules of court. Masters are appointed by the provincial government. As a result, while Masters sit in a superior court, they do not have the “inherent jurisdiction” of the judges of those courts, who are appointed by the federal government and whose authority is derived from the Constitution of Canada and the Crown. Their jurisdiction is usually limited to procedural and Interlocutory matters heard in chambers. Masters commonly also sit as Registrars in Bankruptcy.
In the Federal Court of Canada, a judicial officer with much the same powers as a Master is called a Prothonotary.
Traditionally a Master is referred to as "Master Smith" or, in court, as "Master". In some jurisdictions, Masters are now referred to as "your honour".
Masters and Prothonotaries are independent judicial officers although they do not have the full level of security of tenure afforded to federally appointed judges.
In Alberta, British Columbia and Manitoba, masters have the same terms of appointment as provincial judges. This was formerly the case in Ontario as well but after the High Court of Justice and District Courts were merged, in 1986 a new office of Case Management Master was created.
In Ontario Case Management Masters have all of the authority of traditional masters as well as additional jurisidction to manage actions and engage in dispute resolution processes. They are appointed by Order in Council and can only be removed for cause by the Chief Justice following a formal disciplinary process. 
In Ontario the distinction between "chambers" and "court" has been abolished. When masters preside they sit as the court and their function is to perform tasks that would otherwise fall to superior court judges. Besides the jurisdiction to hear most interlocutory motions in civil matters, case management masters in Ontario also preside at status hearings, case conferences and pre-trials. They frequently act as referees to hear trials in construction lien matters, mortgage references or issues referred by judges. Case management masters also provide dispute resolution services and sit as Registrars in Bankruptcy.