outlines the law that applies to new weapon technologies. It starts by noting the legal obligation for all states to review the lawfulness of new weapons and the more extensive duties of states party to Additional Protocol I. The customary superfluous injury and indiscriminate weapons principles are explained, customary and treaty rules protecting the natural environment and addressing its employment as a weapon are considered. Thereafter, specific weapon prohibitions and restrictions e.g. in relation to poisons, asphyxiating gases, chemical weapons, biological weapons, certain fragmentation weapons, particular kinds of mine and booby-trap, incendiary weapons, lasers, cluster munitions and specified types of bullet are set forth. The criteria that determine the lawfulness of weapons and that must therefore be applied during weapon reviews are noted and lessons based on past, less than successful attempts to regulate what then were emerging technologies are suggested.