Thisvolumeisacompletelynewversionofthebookunderthesametitle,whichappearedin1981asVolume9intheseries"ProgressinMathematics,"andwhichhasbeenoutofprintforsometime.Thatbookhaditsorigininnotes(takenbyHassanAzad)fromacourseonthetheoryofLinearalgebraicgroups,givenattheUniversityofNotreDameinthefallof1978.Theaimofthebookwastopresentthetheoryoflinearalgebraicgroupsoveranalgebraicallyclosedfield,includingthebasicresultsonreductivegroups.Adistinguishingfeaturewasaself-containedtreatmentoftheprerequisitesfromalgebraicgeometryandcommutativealgebra.