Kihnu is an island in the Baltic Sea. With an area of 16.4 km2 (6.3 sq mi), it is the largest island in the Gulf of Riga and the seventh largest island of Estonia. With a length of 7 km (4.3 mi) and width of 3.3 km (2.1 mi), the island's highest point is 8.9 metres (29.2 ft) above sea level.

The Gulf of Riga, Bay of Riga, or Gulf of Livonia is a bay of the Baltic Sea between Latvia and Estonia.