Internet platforms have become important fora of public debate, offering tools for increased democratic participation and engagement. The central role of internet platforms enables them to wield considerable control over online speech. Platforms effectively have the power to decide what content to disseminate and what content to remove. The same power is used to adjust content according to the profiles of users developed on the basis of their personal data. Recent scandals have shown that platforms can be misused as instruments of misinformation, propaganda and manipulation. Policy makers try to address the issue by regulating or by incentivising platforms to adopt codes of conduct.