Historical Security Research and the Security of Peace The article investigates ‚security of peace‘ and introduces the methodology of historical security studies developed in the Marburg SFB research project “Dynamics of Security”. What did political actors mean when they spoke of security and what were the political implications and consequences? The chapter answers this question by focusing on two diplomatic and political tools which were widely regarded as key instruments in any attempt to guarantee peace: hostage taking and dynastic marriages. In each case, the central aim was the security of special treaties (peace treaties, but also offensive alliances) rather than a ‚universal‘ peace. That involved perceived threats to the dynastic succession or to the confessional status quo or geographical integrity of a territory. Dynastic marriages helped mitigate these threats. Taking hostages, by contrast, was primarily used as part of a broader security-enhancing repertoire, for example in military and colonial contexts.