This article presents an initial discussion of the political and legal challenges associated with weaponised technologies in three interconnected areas that may impinge upon the ability to protect civilian populations during peace and war and imperil international security: armed unmanned combat aerial vehicles (commonly known as drones); autonomous weapons systems (known as ‘killer robots’); and the potential militarisation of cyberspace, or its use as a weapon, and the operation of drones and killer robots in the cyber domain. Supporting the argument that the world is ‘facing new methods of warfare’ and that international security governance and law are not keeping up, the article provides an overview and interpretation of three technologies in connection with aspects of five branches of law: state responsibility, use of force, international humanitarian law, human rights law, and law of the commons. I argue therefore that ‘preventive security governance’ could be a strategy to curtail uncertainty in the preservation of stability and international order. I define ‘preventive security governance’ as the codification of specific or new global norms, arising from existing international law that will clarify expectations and universally agreed behaviour on a given issue-area. This is essential for a peaceful future for humanity and for international order and stability.