The Crown Office and Procurator Fiscal Service (Scottish Gaelic: Oifis a' Chrùin agus Seirbheis Neach-casaid a' Chrùin) is the independent public prosecution service for Scotland, and is a Ministerial Department of the Scottish Government. The department is headed by His Majesty's Lord Advocate, who under the Scottish legal system is responsible for prosecution, along with the sheriffdom procurators fiscal. In Scotland, virtually all prosecution of criminal offences is undertaken by the Crown. Private prosecutions are extremely rare.

The Service's jurisdiction covers all of Scotland, and includes investigation and prosecution of criminal offences, sudden or suspicious deaths, and criminal conduct by the police. It also includes assessment and possession of bona vacantia and treasure trove. The Lord Advocate is assisted by the Solicitor General for Scotland, both of whom are Law Officers. The day-to-day running of the Service is carried out by the Crown Agent & Chief Executive and an executive board who are based in the service headquarters at Crown Office in Chambers Street, Edinburgh. The Service employs both civil servants who carry out administrative and other duties and solicitors and advocates who represent the Crown in Court.

The history of the Lord Advocate, and the resulting department of the Crown Office, is somewhat obscure. There are references on record to a king's procurator-fiscal in 1434 and 1457, and a queen's advocate in 1462. An office of king's advocate dates from 1478 but between 1478 and 1494 there are references to "advocates" (unnamed) and it is only from 1494 that one can be sure that there was a single king's advocate as the normal representative of the king in treason trials and in civil litigation. The office thus dates back to mediaeval times, with the earliest Lord Advocate being John Ross of Montgrenan, whom the King appointed as his commissioner at a hearing in Stirling in 1476, then as procurator for another case in Edinburgh in the following year.

The history of the procurator fiscal is similarly difficult to set down with exactness, though the role has developed significantly over time. The first documentary reference appears in the Records of the Parliament of Scotland for 22 August 1584, naming several procurators fiscal in Edinburgh. The fiscal was an officer appointed by, and accountable to, the Sheriff, who by the 18th century was responsible for most prosecutions in local areas. By the 19th century, advocates depute were first appointed, to assist him in conducting cases in the High Court of Justiciary and the Crown Office was first established. This became the centre of the prosecution system, and it was to the Lord Advocate now to whom the procurators fiscal were responsible, evidenced by the "Book of Regulations" issued by him to procurators fiscal providing instructions about how to conduct their business. The Book of Regulations is still used today in providing the framework for local prosecution in Scotland.

As well as departmental management responsibility, the Lord Advocate is directly responsible for prosecuting the most serious crimes, in the High Court of Justiciary at first instance and the Court of Criminal Appeal. Unless the cases are of especial importance, such as the Lockerbie trial held at Camp Zeist in the Netherlands, the prosecutions are normally (but not always) led by advocates depute, who are known collectively as Crown counsel and are experienced members of the Faculty of Advocates normally appointed for a limited period of three years. Their decision to prosecute in this way is taken in the light of the procurator fiscal's recommendations and a report prepared by the police, and any such reports are subject to the direction of the Lord Advocate. This prosecutorial role cannot be removed from her by the Scottish Parliament.

The Lord Advocate is the senior of the two Scottish Law Officers, and is the chief legal adviser to the Scottish Government as well as representing its ministers in civil proceedings. He is also responsible under the Scotland Act 1998 for ensuring that each Act of the Scottish Parliament is within the legislative competence of that Parliament. Additionally, the Lord Advocate and the Solicitor General for Scotland are ex officio entitled to participate (but not vote) in proceedings of the Scottish Parliament to the extent permitted by standing orders. The Solicitor General can act as the deputy for the Lord Advocate.

The Lord Advocate is one of the Great Officers of State in Scotland and one of the Scottish Ministers, though since 23 May 2007 the Lord Advocate has not attended the cabinet of the Scottish Government. The position of Lord Advocate has been the subject of controversy, most notably sparked by Scottish High Court judges, wanting the ministerial and prosecutorial role to be separated.

The Crown Agent is the principal legal adviser to the Lord Advocate on prosecution matters, as well as serving as chief executive for the department. The Crown Agent acts as the principal legal adviser to the Lord Advocate in all legal proceedings in which the Lord Advocate appears as representing his or her own department, and issues general instructions from and on behalf of the Lord Advocate for the guidance of Crown counsel, procurators fiscal, sheriff clerks and other public officials. The Crown Agent also transmits instructions from Crown counsel to procurators fiscal about prosecutions, and, subject to the direction of the Principal Clerk of Justiciary, arranges sittings of the High Court of Justiciary. At trials in the High Court in Edinburgh, the Crown Agent attends as instructing solicitor. The Crown Agent is ultimately responsible for serious crime committed and re–offending as well as ensuring all deaths reported to the procurator fiscal service are investigated whilst providing support services and information to victims and witnesses.