A concept that has been bouncing around the psychological literature for some time is that of resilience, the idea that individuals can exhibit positive adaptation in the process of experiencing adverse life events. Simply put, one might say resilient people bounce back from negative events. The New Shorter Oxford English Dictionary (1993) contains the following definitions of resilience:1 a The action or act of rebounding or springing back. b Recoil from something; revolt. 2 Elasticity; spec. the amount of energy per unit volume that a material absorbs when subjected to strain. 3 The ability to recover readily from, or resist being affected by, a setback, illness, etc. (p. 2562) These definitions constitute an interesting overlap of physical and psychological meanings. This overlap creates an intentional metaphor of elasticity when used to describe a short-term, intraindividual psychological process. However, positive adaptation and elasticity may have subtly differing meanings.In this chapter, we examine some models that can describe two physical properties, elasticity and damping, that are used to describe resilient physical systems. We propose that models such as these are important to consider if one wishes to make a claim of construct validity for the overlap between the physical and psychological meanings of resilience. In other words, our argument is that if we wish to measure how someone "bounces back," we need models that can parameterize the bounce. If we fit models describing components of physical elasticity to intraindividual psychological adaptation in the presence of stress and find that parts of the model do not provide explanatory power, then we would like to know what parts of the physical elasticity metaphor for resilience should be modified or discarded. Finally, by taking the physical elasticity metaphor seriously, we introduce a language for expressing differences between models that can help clarify our thinking about different forms of intraindividual adaptation to stress.