The Single Electricity Market (SEM) is the wholesale electricity market for the island of Ireland.  First going live on 1 November 2007, the market trades wholesale electricity in Ireland and Northern Ireland on an All-Island basis.

The market is jointly regulated by the Utility Regulator and the Commission for Regulation of Utilities.  The decision-making body which governs the market is the SEM Committee (SEMC).

The SEM recently underwent significant change.  Energy markets across Europe are coming together with the aim of creating a fully liberalised internal electricity market.  New market arrangements came into place on 1 October 2018 and are designed to deliver increased levels of competition which should help put a downward pressure on prices as well as encouraging greater levels of security of supply, transparency and investment.