The statics and dynamics of smectic C (and C*) liquid crystals has been a l
ong-standing topic for investigations. All the previous descriptions, howev
er, have been restricted in some sense. Either the theories were linear, or
Bat layers were assumed, or the layer thickness was taken to be constant,
or only statics was considered, or the description (in the chiral case) inc
luded terms not compatible with layering. Here we will give a nonlinear hyd
rodynamic theory, which applies to strongly curved layers, non-flat 'ground
' states, strongly compressed layers as well as strongly deformed director
orientations. Some discrepancies between previous theories are resolved. (C
) 1999 Elsevier Science B.V. All rights reserved.