This article presents a descriptive analysis of the precautions that are required of all belligerents in order to ensure the protection of civilian populations and objects against the effects of hostilities. The author argues that both the attacker and the defender must take precautions to avoid, or at least minimize, collateral casualties and damage. The rules imposing such precautionary measures represent clear standards of conduct. This is true even though they are worded in flexible terms to take into account the reality that mistakes or misjudgements are inevitable, and that the balance between military and humanitarian interests is not always easy to reach.