Research on the psychological consequences of social network site (SNS) use has produced mixed results. Some studies suggest that SNS (particularly Facebook) use is beneficial, whereas others suggest that it is harmful. What can account for these mixed results? This article reviews the literature on this topic and offers self-presentation as a framework for understanding the differential effects of SNS use on psychological well-being. There are 2 key points from our perspective. First, Facebook users tend to present themselves positively on SNSs. Second, the psychological impact of SNS use will depend upon whether a user’s activities are self-focused or other-focused. Focusing on one’s own positively presented self-image generally leads to beneficial outcomes, whereas focusing on others’ idealized images typically leads to harmful outcomes. Practical recommendations for SNS use are offered.