  We give a topological framework for the study of Sela's limit groups: limit
groups are limits of free groups in a compact space of marked groups. Many
results get a natural interpretation in this setting. The class of limit groups
is known to coincide with the class of finitely generated fully residually free
groups. The topological approach gives some new insight on the relation between
fully residually free groups, the universal theory of free groups,
ultraproducts and non-standard free groups.
