Crises in obesity and changes in the environment illustrate the need to change problematic behaviors and lifestyles in large segments of the population. This article uses social psychological theory and research to understand methods for facilitating lifestyle change. A basic assumption in the social psychological perspective is that the environment and the person interact to determine behavior. Both factors are important for understanding “upstream” and “downstream” approaches to lifestyle change (McKinlay, 1993; Verplanken & Wood, 2006) and consideration of one factor without the other may be disastrous. We review evidence from within and outside of the health context to illustrate the upstream and downstream approaches and then describe implications for public policy and intervention. The evidence and recommendations encompass a wide range of behaviors, ranging from speeding and intoxicated driving to eating an unhealthy diet and energy conservation. When armed with the relevant social psychological theory and evidence, lifestyle change campaigns are likely to be successful.