Contemporary liberal theorists generally support open borders and some argue that liberalism is incompatible with substantive immigration control. We argue that it has not been shown that there is an inconsistency in the idea of a liberal state enforcing such controls and that it may be obligatory for a liberal state to impose substantive restrictions on immigration. The immigration control on which we focus is that concerning people from societies that resemble closed societies, particularly those in which Islamic fundamentalism is (...) endemic. We suggest that, if the threat we envision is real, then a liberal state has a right to limit immigration from such societies. (shrink)