Social media technologies (such as Facebook, Twitter, Google, YouTube, Snapchat and Instagram) have brought about radical changes in how the media systems of liberal democracies operate. The platform providers have become powerful actors in the operation of the media system, and in how it connects to political processes. At the same time, these companies claim political neutrality, because most of their content is created by their millions of users – perhaps creating far greater citizen vigilance over government and politicians. Ros Taylor and the Democratic Audit team examine how far the UK’s social media system operates to support or damage democratic politics. Does it help to ensure a full and effective representation of citizens’ political views and interests?