  Lanthanide atoms have an unusual electron configuration, with a partially
filled shell of $f$ orbitals. This leads to a set of characteristic properties
that enable enhanced control over ultracold atoms and their interactions: large
numbers of optical transitions with widely varying wavelengths and transition
strengths, anisotropic interaction properties between atoms and with light, and
a large magnetic moment and spin space present in the ground state. These
features in turn enable applications ranging from narrow-line laser cooling and
spin manipulation to evaporative cooling through universal dipolar scattering,
to the observation of a rotonic dispersion relation, self-bound liquid-like
droplets stabilized by quantum fluctuations, and supersolid states. In this
short review, we describe how the unusual level structure of lanthanide atoms
leads to these key features, and provide a brief and necessarily partial
overview of experimental progress in this rapidly developing field.
