  We gauge the non-abelian isometries of a sigma model with boundaries. Forcing
the field strength of the gauge fields to vanish renders the gauged model
equivalent to the ungauged one provided that boundary conditions are taken into
account properly. Integrating out the gauge fields gives the T-dual model. We
observe that T-duality interchanges Neumann (or mixed) boundary conditions with
Dirichlet boundary conditions.
