Psychology and social media are topics about which many of us have opinions about, given how intimately we are involved with both. This book is about trying to tease out the relationships between the two by exploring case studies and scholarly research. Consequently, its first chapter introduces the broad outlines of social media’s psychological aspects. A brief history is presented, comparing social media with other forms of communication and self-technologies. Social media is defined in a psychological sense as meaning online services which encourage their users to digitise and publicly share previously private personal information. The chapter also distinguishes essential terms like social media, social network and social networking site. The state of social media across the world today is illustrated, in addition to the general situation regarding the scientific knowledge base on its psychological implications. Chapter 1 closes by presenting an overview of the chapters to come, each based around a core feature of social media services: profiles, connections, updates, media, messages and values.