Employinglightweight,tool-basedcodereviewofcodechanges(akamoderncodereview)hasbecomethenormforawidevarietyofopen-sourceandindustrialsystems.Inthispaper,wemakeanexploratoryinvestigationofmoderncodereviewatGoogle.Googleintroducedcodereviewearlyonandevolveditovertheyears;ourstudyshed