This subproject of the interdisciplinary project "Peer Productivity in Web 2.0 Environments" deals with the economic analysis of social links in online networks. It first and foremost considers Wikis, in particular the platform Wikipedia, but also focuses on Q&A forums or interactive online markets (e.g. including evaluation and recommendation systems). The goal of the project is to study peer effects and knowledge spillovers that arise in the knowledge creation online. In this study we cooperate with psychologists from the Knowledge Media Research Center in Tübingen. Moreover, in cooperation with computer scientists, the project continues to develop a technical infrastructure that allows to explore large data sets in a flexible way and to make them accessible to social science analysis.The project is part of the Leibniz-ScienceCampus Tübingen.