  Atoms with a large scattering length have universal low-energy properties
that do not depend on the details of their structure or their interactions at
short distances. In the 2-atom sector, the universal properties are familiar
and depend only on the scattering length. In the 3-atom sector for identical
bosons, the universal properties include the existence of a sequence of shallow
triatomic molecules called Efimov trimers and log-periodic dependence of
scattering observables on the energy and the scattering length. In this review,
we summarize the universal results that are currently known. We also summarize
the experimental information that is currently available with an emphasis on
3-atom loss processes.
