This article is concerned with an Irish law dating from 697 AD, called Lex Innocentium or the Law of the Innocents. It is also known as Cáin Adomnáin, being named after Adomnán (d. 704), ninth Abbot of Iona, who was responsible for its drafting and promulgation. The law was designed to offer legislative protection to women, children, clerics and other non-arms-bearing people, primarily, though not exclusively, in times of conflict. Today, the laws of war fall into two categories: those attempting to regulate when it is lawful or just to go to war, now called jus ad bellum, and those attempting to limit the awful effects of war by stipulating how it should be properly conducted (for instance, in providing for non-combatant immunity), now called jus in bello. By proscribing the killing and injuring of non-arms-bearing people, Lex Innocentium is an in bello law, and by virtue of its being the first known such law, Adomnán, its author, is the father of Western jus in bello.