  Toroidal backgrounds for bosonic strings are used to understand target space
duality as a symmetry of string field theory and to study explicitly issues in
background independence. Our starting point is the notion that the string field
coordinates $X(\sigma)$ and the momenta $P(\sigma)$ are background independent
objects whose field algebra is always the same; backgrounds correspond to
inequivalent representations of this algebra. We propose classical string field
solutions relating any two toroidal backgrounds and discuss the space where
these solutions are defined.
  String field theories formulated around dual backgrounds are shown to be
related by a homogeneous field redefinition, and are therefore equivalent, if
and only if their string field coupling constants are identical. Using this
discrete equivalence of backgrounds and the classical solutions we find
discrete symmetry transformations of the string field leaving the string action
invariant. These symmetries, which are spontaneously broken for generic
backgrounds, are shown to generate the full group of duality symmetries, and in
general are seen to arise from the string field gauge group.
