  In this paper we establish the endoscopic classification of tempered
representations of quasi-split unitary groups over local fields, and the
endoscopic classification of the discrete automorphic spectrum of quasi-split
unitary groups over global number fields. The method is analogous to the work
of Arthur on orthogonal and symplectic groups, based on the theory of endoscopy
and the comparison of trace formulas on unitary groups and general linear
groups.
