This chapter summarizes key findings from experimental or quasi-experimental studies on the determinants of savings through employer-sponsored retirement benefits plans. Research shows that default rules and the ability to commit now for the future can have a dramatic impact on enrollment rates. Analysis also shows that enrollment decisions can be influenced by peer decisions, as well as information provided by the employer. We also identify gaps in existing knowledge and propose new randomized experiments which could be conducted in the workplace that would fill important gaps in our understanding of the determinants of retirement savings.