Saimaa, or Saimen in Swedish, is a lake in southeastern Finland. At 1,147 square km (443 square miles), it is the largest lake in Finland, and the fifth largest in Europe. Major towns on the lakeshore include Lappeenranta, Imatra, Savonlinna and Mikkeli. The river Vuoksi flows from Saimaa to Lake Ladoga.

The Saimaa Canal from Lappeenranta to Vyborg binds Saimaa to the Gulf of Finland. Other canals bind Saimaa to smaller lakes in Eastern Finland and form a network of waterways. These waterways are mainly used to transport wood, minerals, metals, pulp and other cargo, but also tourists use the waterways.

One of the two fresh water seal species, the Ringed Seal lives in Saimaa.