Life is uncertain, and uncertainty is particularly relevant to the challenges posed by climate change to society and natural environments. In this introductory chapter, we summarize the main components of uncertainty relating to climate change and how they affect the decisions we need to make. We explain the deliberate orientation of this book, specifically, starting from the point of view of decision-makers who are striving to manage risks associated with climate change (alongside other human drivers of global change). We explore the different ways uncertainty is viewed and managed, such as when assessing socioeconomic vulnerabilities and impacts of climate change or evaluating options for mitigating and adapting to climate change. We also consider the difficulties involved in communicating the uncertainties of climate change to various audiences. Above all, we stress that uncertainty is not an excuse for inaction. There are now many tools and frameworks that can support mitigation and adaptation decisions, despite deep uncertainty about the future.