Thisvolumedescribestheadvancesinthequantumtheoryoffieldsthathaveledtoanunderstandingoftheelectroweakandstronginteractionsoftheelementaryparticles.Theseinteractionshaveallturnedouttobegovernedbyprinciplesofgaugeinvariance，sowestarthereinChapters15-17withgaugetheories，generalizingthefamiliargaugeinvarianceofelectrodynamicstonon-AbelianLiegroups.　　Someofthemostdramaticaspectsofgaugetheoriesappearathighenergy，andarebeststudiedbythemethodsoftherenormalizationgroup.ThesemethodsareintroducedinChapter18，andappliedtoquantumchromodynamics，themodernnon-Abeliangaugetheoryofstronginteractions，andalsotocriticalphenomenaincondensedmatterphysics.Chapter19dealswithgeneralspontaneouslybrokenglobalsymmetries，andtheirapplicationtothebrokenapproximateSU(2)xSU(2)andSU(3)xSU(3)symmetriesofquantumchromodynamics.Boththerenormalizationgroupmethodandbrokensymmetriesfindsomeoftheirmostinterestingapplicationsinthecontextofoperatorproductexpansions，discussedinChapter20.　　Thekeytotheunderstandingoftheelectroweakinteractionsisthespontaneousbreakingofgaugesymmetries，whichareexploredinChap-ter21andappliedtosuperconductivityaswellastotheelectroweakinteractions.Quiteapartfromspontaneoussymmetrybreakingisthepossibilityofsymmetrybreakingbyquantum-mechanicaleffectsknownasanomalies.AnomaliesandvariousoftheirphysicalimplicationsarepresentedinChapter22.ThisvolumeconcludeswithadiscussioninChapter23ofextendedfieldconfigurations，whichcanariseeitherasnewingredientsinphysicalstates，suchasskyrmions，monopoles，orvortexlines，orasnon-perturbativequantumcorrectionstopathintegrals，whereanomaliesplayacrucialrole.