An Order-in-Council is an executive order issued in Commonwealth Realms operating under the Westminster system. They are formally made in the name of the Queen (or the Governor-General acting on her behalf) by the Cabinet, which is a committee of the Privy Council (the Queen-in-Council or the Governor-in-Council). Orders in Council are, legally speaking, the exercise of the Royal Prerogative in areas where this still applies. Sometimes Acts of Parliament specify that something shall be done by an Order in Council, but this (like the Royal Prerogative generally) is being replaced by Statutory Instruments.

Orders in Council in the United Kingdom are used, therefore, for matters which still fall within the Royal Prerogative: dealing with servants of the Crown, such as the standing orders for civil servants, making appointments in the Church of England and dealing with international relations.

Whilst the Northern Ireland Assembly remains suspended, much Northern Ireland legislation is made by Order-in-Council.

In the rest of the Commonwealth they are used to carry out any decisions made by the cabinet and the executive that would not need to be approved by parliament.

Although the orders are nominally made by the Queen or her representative, her assent is now purely formality. What actually happens is that the Lord President of the Council (a cabinet minister) reads out batches of Orders-in-Council, which will have been written by the government, in front of the monarch or representative, who, after every couple of orders, says 'Agreed'. They then pass into law, where they are fully effective, although the usual rules of English Law in respect of the dominance of Parliament over the Royal Prerogative apply, so they can be overruled by Acts of Parliament or Statutory Instruments. Of course, since the government writes these too, that now never occurs.

Traditionally, orders in council are used as a way for the prime minister to make political appointments, but they can also be used to issue simple laws as a sort of decree. Often in times of emergency a government may issue legislation directly through orders in council, forgoing the usual parliamentary procedure. However, most orders in council of this sort are usually eventually formalized according to the traditional lawmaking process. Occasionally orders are used to effectively reverse court decisions without involving parliament, for example to prevent the Ilois islanders returning to Diego Garcia from which they had been unlawfully exiled.