This book is the product of a worldwide collaboration among UN water resources programs, prominent national water resources operating agencies and selected academic specialists. It deals directly with some of the most difficult problems water engineers, managers and decision makers face when designing and implementing water resources infrastructure under new patterns of climate variability. Projecting the probabilities and risks associated with such events has traditionally been central to water resources planning and modeling. Such projections have been keys to social, environmental, economic, and financial investment decisions making. However, our contemporary world has called into question some of the traditional methods and approaches to formulating such projections. This collection provides practical grounding in selected advances already in place and practiced by leading institutions; advances that could be readily adapted by the water resources engineering and design professionals to better deal with risk and uncertainty in a non-stationary climate world. We believe this book opens important venues which can help to enhance the water and climate dialogues worldwide.