A great deal of political debate takes place in social media and also in these debates legal expertise (or the lack of it) matters. This chapter discusses the question of legal expertise behind blogs and social media and their policy impact through the example of Verfassungsblog, established in 2009 as a journalistic and academic forum of debate on topical events and developments in constitutional law and politics in Germany, the emerging European constitutional space and beyond. In less than ten years the Verfassungsblog has become a key interface with more than 500 authors. The blog sees itself as an interface between the academic expert discourse, on the one hand, and the political public sphere, on the other. Is legal expertise in social media merely an academic exercise, or does it have societal impact? Can it influence actual policy outcomes?