In the United States, the residential sector accounts for a significant proportion of the greenhouse gas (GHG) emissions produced each year. Sixty-two percent of vehicle emissions come from passenger cars and light-duty trucks, and one-quarter of non-transportation emissions come from residential sources. Many individual-level behaviors that contribute to these emissions could be modified, for example, by purchasing compact fluorescent bulbs (purchasing behaviors), increasing one's refrigerator temperature (nonpurchasing, one-time behaviors), regularly shutting off the lights (repeated behaviors or habits), or insulating one's hot water heater (complex behaviors that require expert assistance or are costly). Changes in such individual-level behaviors may play an important role in slowing climate change.