Is polarisation a fundamental threat to the open society? Are the divisions that run through societies and separate them into two (or more) more or less hostile groups problems to be solved? Or are they the corollaries of a vibrant democratic system that might legitimately be called an 'open society'? These are the questions Christof Royer seeks to explore in this Essay. His argument unfolds through a reinterpretation of Karl Popper's conception of open society as a democratic idea, characterised by an appreciation of genuine human plurality and diversity that make 'critical encounters with the other side' possible (and desirable); this conception of open society also recognises the productive and progressive potential of social and political conflicts. For that reason, political polarisation cannot be regarded as a lethal threat to open societies. By contrast, 'belief polarisation', with its Manichean orientation and anti-political tendencies, is a much more serious threat. It follows that advocates of open society should avoid the temptation to solve the 'problem' of political polarisation - they should accept it as the price to be paid for the 'imperfect ideal' of open society. However, they should take steps to reduce belief polarisation through the active creation of spaces of critical encounters with the other side.