  We calculate ground state properties (energy, magnetization, susceptibility)
and one-particle spectra for the $S = 1$ Heisenberg antiferromagnet with
easy-axis or easy-plane single site anisotropy, on the square lattice. Series
expansions are used, in each of three phases of the system, to obtain
systematic and accurate results. The location of the quantum phase transition
in the easy-plane sector is determined. The results are compared with spin-wave
theory.
