Mensa (the Table) is a southern constellation which was first introduced by Nicolas Louis de Lacaille under the name Mons Mensae (Latin for "the table mountain"). This specifically refers to Table Mountain in South Africa, where Lacaille made important early observations of the southern sky. It contains no bright stars, with Alpha Mensae its brightest star at a barely visible magnitude 5.09, but it does contain part of the Large Magellanic Cloud (the rest being in Dorado).

The constellation covers a keystone-shaped wedge of sky stretching from approximately 4h to 7.5h of right ascension, and -71 to -85.5 degrees of declination. Other than the south polar constellation of Octans, it is the most southerly of constellations. As a result, it is essentially unobservable from the Northern Hemisphere. Besides those already mentioned, its other neighbouring constellations are Chamaeleon, Hydrus and Volans.

The first images taken by the Chandra X-Ray Telescope were of PKS 0637-752, a quasar in Mensa with a large gas jet visible in both optical and x-ray wavelengths.