Accelerating change is transforming our world, from the prosaic (such as the effect of information technology on the way we use the telephone) to the profound (such as the effect of greenhouse gases on the global climate). Some of these changes amaze and delight us; others impoverish the human spirit and threaten our survival. More important, thoughtful leaders increasingly suspect that the tools they have been using have not only failed to solve the persistent problems they face, but may in fact be causing them. All too often, well-intentioned efforts to solve pressing problems create unanticipated side effects. Our decisions provoke unforeseen reactions. The result is policy resistance, the tendency for interventions to be defeated by the response of the system to the intervention itself. From California’s failed electricity reforms, to road building programs that create suburban sprawl and actually increase traffic congestion, to the latest failed change initiative in your company, our best efforts to solve problems often make them worse. Table 1 lists some examples, including economic, social, and environmental issues.