Lutetium (Lu) is a metallic chemical element with atomic number 71. It is the last element in the lanthanide series. The only stable lutetium isotope is ¹⁷⁵Lu, with 71 protons and 104 neutrons.

Lutetium shares chemical properties with most other rare earth metals, but since it is more rare than most of the others ones, and therefore also more expensive, it doesn't have that many industrial applications.