At its most elemental level, human development consists of constancy and change in quantitative and qualitative aspects of behavior and functioning. The science of human development therefore illuminates the causes, mechanisms, and consequences of constancy and change in behavior and functioning. This chapter epitomizes the complexity of human development as a process of constancy and change throughout life. It was a handful of pioneering psychologists—Norman Garmezy, Emmy Werner, and Michael Rutter—primarily interested in child development who bridged the study of risk and resilience and brought this dual focus into the science of human development. Notwithstanding the growing corpus of findings, the field of risk and resilience research in human development has recently undergone a period of internal, critical reflection. In sum, the study of risk and resilience is now a vibrant and significant part of the study of human development.