The concepts clan and region are central to the theory of 2-structures
. Clans form the cornerstone of the decomposition theory and the notio
n of a region underlies the representation theory for 2-structures. Th
is paper examines in depth the basic properties of the two concepts an
d the relationship between them. Also, a characterization of regions f
or angular 2-structures and a morphic characterization of regions in u
niform 2-structures are obtained.