  We focus on non-linear realizations of local supersymmetry as obtained by
using constrained superfields in supergravity. New constraints, beyond those of
rigid supersymmetry, are obtained whenever curvature multiplets are affected as
well as higher derivative interactions are introduced. In particular, a new
constraint, which removes a very massive gravitino is introduced, and in the
rigid limit it merely reduces to an explicit supersymmetry breaking. Higher
curvature supergravities free of ghosts and instabilities are also obtained in
this way. Finally, we consider direct coupling of the goldstino multiplet to
the super Gauss--Bonnet multiplet and discuss the emergence of a new scalar
degree of freedom.
