The reach of social media is prodigious. Its ubiquitous nature has reshaped the ways in which government agencies can communicate with citizens. But amidst the rush to embrace the opportunities of Twitter, Facebook and other platforms, governments have had to lay down rules to govern how and when public service departments should use social media. This article undertakes a comparative analysis of the formal rules and guidelines in place across four Westminster jurisdictions – Australia, New Zealand, Canada and the UK – to identify the types of behaviours and activities that are seen as desirable when public servants are reaching out to the wider public through social media. The article argues that the horizontal communication patterns associated with social media are fundamentally at odds with the hierarchical structures of the Westminster system of government.