Scenarios are a methodology of futures and foresight research that has been established for more than half a century. Despite the rich literature on scenarios and ways of constructing them, the current scenario methodologies, current approaches to scenario constructions are often not well aligned with the needs of policymakers. Emerging technologies that are likely to achieve high social relevance in the short to mid-term future and that call for quick policy interventions are difficult to reflect using current scenario approaches. We have therefore developed a new type of scenario that we call a policy scenario. This paper develops the principles and justification for policy scenarios. We provide a detailed description of how they can be constructed, focusing on their key characteristics of policy requirements, plausibility, probability, credibility, expertise, objectivity and legitimacy. Following our stakeholder-based approach allows researchers to construct scenarios that are uniquely suited to inform policymakers and, in effect, the policy development process.