Erbium (Er) is a metallic chemical element with atomic number 68. It is one of the rare earth metals, and like several other rare earth metals it is named after Ytterby, the Swedish village where it was first discovered.

There are several naturally occurring erbium isotopes, but the most abundant one is ¹⁶⁶Er, with 68 protons and 98 neutrons.

Erbium has quite a wide range of different applications, for example it's used in lasers, in sunglasses and in nuclear reactor control rods.