  Halo nuclei are characterized by a few weakly bound halo nucleons and a more
tightly bound core. This separation of scales can be exploited in a few-body
description of halo nuclei, since the detailed structure of the core is not
resolved by the halo nucleons. We present an introduction to the effective
(field) theory for low-energy properties of halo nuclei. The focus is on halos
with S-wave interactions for which universal properties are most pronounced.
The special role of the unitary limit is illustrated using the example of
multineutron systems and the Efimov effect as a universal binding mechanism for
halo nuclei. Connections to ultracold atoms and hadron physics are highlighted
and extensions to higher partial waves, Coulomb forces and nuclear reactions
are briefly touched upon.
