Why do we use social networking sites like Facebook, and what personality traits do people who are most active in such social networks possess? This book provides empirically grounded answers to these questions as one of the first in its field. A thorough examination of the architecture and functionalities of social networking sites, as well as the current state and developmental trends in 21st-century society, lays the groundwork for investigating the research questions. Based on a Uses-and-Gratifications approach tailored to the research subject and current conditions, the two guiding questions are first analyzed theoretically and then empirically: What needs and motives drive people to use social networking sites, and what personality traits characterize particularly intensive users of social networks? Using Facebook as a prototype and a specially designed online survey, the reasons for participation in social networking sites and the attributes of particularly active members are identified, followed by suggestions for future studies in this area.