  The MARS code is under continuous development and has recently undergone
substantial improvements that further increase its reliability and predictive
power in numerous shielding, accelerator, detector and space applications. The
major developments and new features of the MARS15 (2004) version described in
this paper concern an extended list of elementary particles and arbitrary heavy
ions and their interaction cross-sections, inclusive and exclusive nuclear
event generators, module for modelling particle electromagnetic interactions,
enhanced geometry and histograming options, improved MAD-MARS Beam Line
Builder, enhanced Graphical-User Interface, and an MPI-based parallelization of
the code.
