What is proportionality? -- Proportionality : a multiplicity of meanings -- Proportionality in the just war tradition -- Proportionality in international humanitarian law -- Proportionality in human rights law and morality -- The uniqueness of jus in bello proportionality -- Countermeasures and counterinsurgency -- Human shields and risk -- Targeted killings and proportionality in law : two models -- The nature of war and the idea of "cyberwar" -- Thresholds of jus in bello proportionality.