  Generalizing Euclidean inner product and Hermitian inner product, we
introduce Galois inner products, and study the Galois self-dual constacyclic
codes in a very general setting by a uniform method. The conditions for
existence of Galois self-dual and isometrically Galois self-dual constacyclic
codes are obtained. As consequences, the results on self-dual, iso-dual and
Hermitian self-dual constacyclic codes are derived.
