21 Lutetia (lew-tee'-sha) is a large Main belt asteroid, about 100 kilometers in diameter.

It was discovered on November 15, 1852 by Hermann Mayer Salomon Goldschmidt at the observatory of Paris. The name Lutetia derives from the Latin name of Paris.

On July 10, 2010 the European Rosetta comet probe will pass the asteroid with a minimum distance of 3000 km on its way to 67P/Churyumov-Gerasimenko.

It will be a rather important flyby, since Lutetia is not only large but also the first metallic M-type asteroid to be visited by a spacecraft. There are serious questions about the metallicity of the M-type asteroids and the probe is expected to settle the issue.

There are two reported stellar occultations by Lutetia: from Malta (1997) and Australia (2003).