High Jet Multiplicity Physics at the LHC Introduction Theoretical Overview The Large Hadron Collider and the ATLAS Experiment Search for New Phenomena in Events with Large Jet Multiplicities Measurement of the Cross Section of Four jet Events Conclusions. . This book describes research in two different areas of state of the art hadron collider physics both of which are of central importance in the field of particle physics. The first part of the book focuses on the search for supersymmetric particles called gluinos. The book subsequently presents a set of precision measurements of “multi jet” collision events which involve large numbers of newly created particles and are among the dominant processes at the Large Hadron Collider (LHC). Now that a Higgs boson has been discovered at the LHC the existence (or non existence) of supersymmetric particles is of the utmost interest and significance both theoretically and experimentally. In addition multi jet collision events are an important background process for a wide range of analyses including searches for supersymmetry.