We study the continuity, smoothing, and convergence properties of Stei
ner symmetrization in higher space dimensions. Our main result is that
Steiner symmetrization is continuous in W-1,W-p (1 less than or equal
to p < infinity) in all dimensions. This implies that spherical symme
trization cannot be approximated in W-1,W-p by sequences of Steiner sy
mmetrizations. We also give a quantitative version of the standard ene
rgy inequalities for spherical symmetrization.