  The procedures of validating simulation of particle physics events at the LHC
are summarized. Because of the strongly fluctuating particle content of LHC
events and detector interactions, particle based Monte Carlo methods are an
indispensable tool for data analysis. Simulation in particle physics is founded
on factorization and thus its global validation can be realized by validating
each individual step in the simulation. This can be accomplished by adopting
results of previous measurements, in - situ studies and models. Important in
particle physics is to quantify how well simulation is validated such that a
systematic uncertainty can be assigned to a measurement. The simulation is
tested for a wide range of processes and agrees with data within the assigned
uncertainties.
