  We present the program SuSpect3 that calculates the masses and couplings of
the Higgs and supersymmetric particles predicted by the Minimal Supersymmetric
Standard Model (MSSM). The model is implemented in both its non-constrained
version, the MSSM, and its constrained versions, such as the minimal
supergravity and the gauge or anomaly mediated supersymmetry breaking models,
in which the soft supersymmetry-breaking parameters obey certain universal
boundary conditions at the high energy scale. The low energy parameters are
then obtained using renormalization group equations and electroweak symmetry
breaking, and all the dominant radiative corrections have been consistently
implemented. SuSpect3 is a major rewrite, in C++ object oriented programming,
of the FORTRAN code SuSpect. It includes all the features of the earlier code
in an improved and updated manner, and involves new options such as compressed
SUSY scenarios, an MSSM-inflation model and the possibility of using the
observed Higgs mass as an input. The main features and the use of the program
are explained.
