During this past century there has been growth in social concern about horrific forms of violence, like ecocide, genocide, modern warfare, ethnic hatred, racism, sexual abuse and domestic violence, and a corresponding growth in the field of peace education where educators, from early child care to adult, use their professional skills to warn fellow citizens about imminent dangers and advise them about paths to peace. This paper traces the evolution of peace education theory from its roots in international concerns about the dangers of war to modern theories based on reducing the threats of interpersonal and environmental violence. This paper reviews ways that peace education has become diversified and examines theoretical assumptions behind five different ways in which it is being carried out at the beginning of the twenty-first century: international education, human rights education, development education, environmental education and conflict resolution education.