  We perform a systematic study of radiative corrections to the masses of the
Higgs bosons in the minimal supersymmetric standard model (MSSM) augmented by a
single gauge singlet, the so-called next-to-minimal supersymmetric standard
model (NMSSM). Our method is based on the one-loop effective potential and
includes effects of top quark, squark, Higgs and Higgsino loops. We discuss the
renormalisation group flows of Yukawa couplings and the upper bound on the
lightest CP-even neutral Higgs boson mass as a function of the heavier stop
mass and top mass. We then give a general discussion of Higgs boson
phenomenology including radiative corrections. We survey as much of the
parameter space of the Higgs sector of the NMSSM as is practicable, and analyse
the full spectrum of Higgs masses and couplings in these regions of parameter
space. Characteristic signatures of the NMSSM such as light charged bosons and
weakly coupled neutral scalars are discussed, as are the relative sizes of the
various radiative corrections. The MSSM is also discussed as a limiting case of
the NMSSM for comparison.
