  In the first part of the talk we discuss T-duality for a free boson on a
world sheet with boundary in a setting suitable for the generalization to
non-trivial backgrounds. The gauging method as well as the canonical
transformation are considered. In both cases Dirichlet strings as T-duals of
Neumann strings arise in a generic way. In the second part the gauging method
is employed to construct the T-dual of a model with non-Abelian isometries.
