TL;DR: In this paper, the authors proved the local and global Arthur conjectures for tempered representations of the unitary group with respect to the discrete automorphic representations of unitary groups.
Abstract: Following Arthur's study of the representations of the orthogonal and symplectic groups, we prove many cases of both the local and global Arthur conjectures for tempered representations of the unitary group This completes the proof of Arthur's description of the discrete series representations of the quasi-split $p$-adic unitary group, and Arthur's description of the tempered discrete automorphic representations of the unitary group, satisfying certain technical conditions