  We clarify the relation between various approaches to the manifestly
T-duality symmetric string. We explain in detail how the PST covariant doubled
string arises from an unusual gauge fixing. We pay careful attention to the
role of "spectator" fields in this process and also show how the T-duality
invariant doubled dilaton emerges naturally. We extend these ideas to
non-Abelian T-duality and show they give rise to the duality invariant
formalism based on the semi-Abelian Drinfeld Double. We then develop the
N=(0,1) supersymmetric duality invariant formalism.
