The House of Schleswig-Holstein-Sonderburg-Glücksburg, also known by its short name as the House of Glücksburg, is the senior surviving branch of the German House of Oldenburg, one of Europe's oldest royal houses. Oldenburg house members have reigned at various times in Denmark, Norway, Sweden, Iceland, Greece, several northern German states, and Russia. It takes its name from the family seat in Glücksburg, a small town in Schleswig-Holstein, Germany.