  In analogy with the Fourier-Stieltjes algebra of a group, we associate to a
unital discrete twisted C*-dynamical system a Banach algebra whose elements are
coefficients of equivariants representations of the system. Building upon our
previous work, we show that this Fourier-Stieltjes algebra embeds continuously
in the Banach algebra of completely bounded multipliers of the (reduced or
full) C*-crossed product of the system. We also introduce a notion of positive
definiteness and prove a Gelfand-Raikov type theorem allowing us to describe
the Fourier-Stieltjes algebra of a system in a more intrinsic way. After a
study of some of its natural commutative subalgebras, we end with a
characterization of the Fourier-Stieltjes algebra involving C*-correspondences
over the (reduced or full) C*-crossed product.
