  This thesis is almost entirely devoted to studying string theory backgrounds
characterized by simple geometrical and integrability properties. The archetype
of this type of system is given by Wess-Zumino-Witten models, describing string
propagation in a group manifold or, equivalently, a class of conformal field
theories with current algebras. We study the moduli space of such models by
using truly marginal deformations. Particular emphasis is placed on asymmetric
deformations that, together with the CFT description, enjoy a very nice
spacetime interpretation in terms of the underlying Lie algebra. Then we take a
slight detour so to deal with off-shell systems. Using a renormalization-group
approach we describe the relaxation towards the symmetrical equilibrium
situation. In he final chapter we consider backgrounds with Ramond-Ramond field
and in particular we analyze direct products of constant-curvature spaces and
find solutions with hyperbolic spaces.
