SSE plc (formerly Scottish and Southern Energy plc) is a multinational energy company headquartered in Perth, Scotland. It is listed on the London Stock Exchange and is a constituent of the FTSE 100 Index. SSE operates in the United Kingdom and Ireland.

Scottish and Southern Energy was formed in September 1998, following a merger between Scottish Hydro-Electric and Southern Electric. In August 2000, Scottish and Southern Energy acquired the SWALEC energy supply business. SWALEC operate exclusively in Wales while SSE operates in Scotland and England.

In July 2004, the company acquired the Ferrybridge and Fiddlers Ferry Power Stations for £250million. In January 2008, it went on to buy Airtricity Holdings, an Irish wind farm business. In August 2009, it agreed to purchase the Uskmouth power station from Welsh Power Group Limited. In April 2010, the company purchased the natural gas exploration and production assets of Hess Corporation in three areas of the United Kingdom Continental Shelf – Everest/Lomond, Easington and Bacton.

In January 2010, Scottish and Southern Energy changed the core company branding from Scottish and Southern Energy to SSE.