With the growing prevalence of wireless communication technologies, social networking sites (SNSs) such as Facebook, Twitter, etc. have become an important venues for interpersonal communication. This chapter provides a detailed overview of the current literature on online social networking with respect to its beneficial and detrimental effects on psychological wellbeing. In particular, it provides empirical evidence for the associations of SNS use with depression, self-esteem, loneliness, subjective wellbeing, social anxiety, attachment, personality traits, and addiction. Furthermore, it identifies the characteristics of individuals who are more prone to social networking, and presents possible mediators and moderators playing a role in the relationship between social networking and mental health. The chapter overall provides a comprehensive guideline to parents, researchers, educators, healthcare, and communication professionals to the issue of online social networking from a psychological perspective.