Search for the term resilience and one finds definitions that vary widely between fields as diverse as ecology, disaster management, developmental psychology, neuroscience, engineering, and economics. Each definition emphasizes a shift in focus from breakdown and disorder to systemic recovery, adaptation, or systemwide transformation during and after exposure to adversity. Seldom, however, have researchers in the natural and human sciences explored the link between the resilience of one system and the resilience of mutually dependent, co-occurring supraordinate and subordinate systems. In this chapter, the author presents a comprehensive theory of resilience that draws together the research done by a range of disciplines where the term resilience has been used as an organizing concept. Using this diverse body of work, this chapter (a) starts with a discussion of definitions that both distinguish fields of resilience research from one another and suggests concurrence in how resilience is understood; (b) presents a model that accounts for the complex reciprocal relationships that enhance the resilience of co-occurring biological, psychological, social, built, and natural systems; (c) reviews seven principles that explain the processes of recovery, adaptation, and transformation of systems under stress; and (4) discusses the implications of a systemic understanding of resilience to the design of interventions that promote change to preferred patterns of functioning when systems are under stress.