HDECAY: a program for Higgs boson decays in the Standard Model and its supersymmetric extension

We describe the Fortran code HDECAY, which calculates the decay widths and the branching ratios of the Standard Model Higgs boson, and of the neutral and charged Higgs particles of the minimal supersymmetric extension of the Standard Model. The program is self-contained (with all subroutines included), easy to run, fast, and it calculates the decay widths and branching ratios according to the current theoretical knowledge.