Lacus Felicitatis (Latin fēlīcitātis, "Lake of Happiness")[1] is a small patch of the lunar surface that has been inundated by flows of lava, leaving a level patch with a lower albedo than the surrounding ground.

It is located in Terra Nivium, an area of continental ground to the north of the Mare Vaporum.

About 70–80 km to the northeast of this area are the Montes Haemus, along the southwestern edge of the Mare Serenitatis.

The selenographic coordinates of the centre of Lacus Felicitatis are 18.5° N, 5.4° E, and it has a maximum extent of 98 km.

In November 2006, it was suggested that Ina was the result of a gas eruption in the last 10 million years.