This article presents an analysis of the role and content of proportionality under contemporary international humanitarian law governing the means and methods of warfare (jus in bello) and is designed to present a legal analysis of proportionality to help provide a context for state practice. The events of Operation ‘Cast Lead’ and the reactions of the international community may be instrumental in determining the role assigned to proportionality in the context of armed conflicts. A study on jus in bello proportionality with reference to Operation ‘Cast Lead’ offers a contribution to a further development of the concept of proportionality and to resolving some of its controversial issues concerning its role and content in order to improve the current compliance of the principle.