Social media are not just a "hype" but have partly restructured public communication. At the same time, the network structure transforms existing institutions of governance. Media law in jurisdictions all over the world tries to cope with these new platforms, their specific risks and the complex allocation of responsibility. We believe that an adequate legal assessment requires an understanding of the new governance structures. Based on work in progress on a study on "governance in social media" the lecture will explore the governance structure based on the four factors of state law, social norms, software design and contract.