This book examines the concept of guilt in the Rome Statute of the International Criminal Court as the most significant factor in determining individual criminal responsibility for the most serious violations of international humanitarian law. The Rome Statute provides a general definition of guilt for the first time in the history of international criminal law, since none of the Statutes of previous international Tribunals contained general rules on this matter. The book also questions the regulation of guilt in the Rome Statute in light of the principle of legality.