War has been an unfortunate reality for almost as long as humankind has existed. As long as there has been conflict, there has been suffering, brutality, and destruction. International humanitarian law itself is one of the older branches of international law, certainly predating both international human rights law and international criminal law. This chapter discusses the substantive rules contained in the Geneva Conventions, particularly those provisions that relate to the issue of collective responsibility. It also describes the considerable historical pedigree of the laws that govern wartime conduct. Although violations of humanitarian law continue, as with any other body of law, few would deny the essential role that international humanitarian law continues to play in the contemporary age.Keywords: Geneva Conventions, international criminal law, international human rights law, wartime conduct