We review the physics basis, main features and use of general-purpose Monte
Carlo event generators for the simulation of proton-proton collisions at the
Large Hadron Collider. Topics included are: the generation of hard-scattering
matrix elements for processes of interest, at both leading and next-to-leading
QCD perturbative order; their matching to approximate treatments of higher
orders based on the showering approximation; the parton and dipole shower
formulations; parton distribution functions for event generators;
non-perturbative aspects such as soft QCD collisions, the underlying event and
diffractive processes; the string and cluster models for hadron formation; the
treatment of hadron and tau decays; the inclusion of QED radiation and
beyond-Standard-Model processes. We describe the principal features of the
ARIADNE, Herwig++, PYTHIA 8 and SHERPA generators, together with the Rivet and
Professor validation and tuning tools, and discuss the physics philosophy
behind the proper use of these generators and tools. This review is aimed at
phenomenologists wishing to understand better how parton-level predictions are
translated into hadron-level events as well as experimentalists wanting a
deeper insight into the tools available for signal and background simulation at
the LHC.Comment: 226 pages, 30 figures, submitted to Physics Report