Interventions for voluntary proenvironmental behavior change usually target a limited number of behaviors and have difficulties in achieving durable change. The EcoTeam Program (ETP) is an intervention package that aims to overcome these flaws. Through a combination of information, feedback, and social interaction in a group--the EcoTeam--participants focus on the environmental consequences of their household behavior. The 3-year longitudinal study found that ETP participants (N=150; mean age 47 yrs) changed half of the 38 household behaviors examined, with corresponding reductions on four physical measures of resource use. These improvements were maintained or enlarged 2 years after completion of the ETP, amounting to savings from 7% on water consumption to 32% on solid waste deposition. A detailed analysis of one behavior, means of transportation, suggests that change can be predicted from the interplay between behavioral intention and habitual performance before participation, and the degree of social influence experienced in the EcoTeam during participation.