  This paper is devoted to the analysis of charged superselection sectors in
the framework of the locally covariant quantum field theories. We shall analize
sharply localizable charges, and use net-cohomology of J.E. Roberts as a main
tool. We show that to any 4-dimensional globally hyperbolic spacetime it is
attached a unique, up to equivalence, symmetric tensor $\Crm^*-$category with
conjugates (in case of finite statistics); to any embedding between different
spacetimes, the corresponding categories can be embedded, contravariantly, in
such a way that all the charged quantum numbers of sectors are preserved. This
entails that to any spacetime is associated a unique gauge group, up to
isomorphisms, and that to any embedding between two spacetimes there
corresponds a group morphism between the related gauge groups. This form of
covariance between sectors also brings to light the issue whether local and
global sectors are the same. We conjecture this holds that at least on simply
connected spacetimes. It is argued that the possible failure might be related
to the presence of topological charges. Our analysis seems to describe theories
which have a well defined short-distance asymptotic behaviour.
