This lecture explores the importance of users in a platform's success, from modeling and motivating massive user groups to creating platforms that leverage their wisdom and work power. It delves into methods of persona creation, exemplified by the transcription platform Transkribus, and discusses the different user personas and their distribution within registered users. The lecture also covers the professional and personal use of platforms, control of access, management of processes, and the quality of output. Additionally, it examines the dynamics of user motivation, re-engagement strategies, and the case studies of Twitter, Quora, and Wikipedia, highlighting the concepts of collectivism, liberalism, and the wisdom of crowds.