A first step in dealing with uncertainty is confronting its existence, ubiquity, and magnitude. A second step is dealing with it when informing assessments and decisions. As the Cold War waned, RAND developed new methods that urged sketching the no-surprises future, listing known branch-style uncertainties, and stretching the imagination to envision potential shocks, good or bad (e.g., Soviet Union disintegration or Saddam Hussein⁰́₉s invasion of Kuwait). Major surprises will nonetheless occur, and some of RAND⁰́₉s most important work on uncertainty has to do with coping with surprise developments. RAND⁰́₉s progress in national security uncertainty analysis benefited from a confluence of developments in computer and software technology, theory and practice in strategic planning and decisionmaking, analytic theory and methods, and theory of complex adaptive systems. Work has emphasized facing up to deep uncertainty in many dimensions, performing exploratory analysis of ⁰́the possibility space, ⁰́₊ identifying regions of that space that pose special risks or opportunities, finding options to improve capabilities, and using portfolio analysis to conceive and compare strategic options for economically dealing with the diversity of challenges. A cross-cutting RAND theme is finding flexible, adaptive, and robust (FAR) strategies. Ultimately, different problems call for different approaches to uncertainty. If the theory of planning under uncertainty and preparing to cope with surprise effectively is difficult and complex, this report makes clear that implementing and maintaining corresponding changes is even more difficult and suggests that policymakers to be constantly vigilant in ensuring that related initiatives are not undercut or allowed to wither.