Across all Abrahamic religions, it has been found that the more religious people are, the more children they have. However, whereas political demographers such as Eric Kaufman have shown that the growth of religious fundamentalist groups that combine relatively high fertility with relatively high retention rates such as the Haredim, Laestadians, Salafi-Islamists, and Orthodox Calvinists poses (long-term) challenges to liberal democracies, philosophers have not considered what, if anything, states may or should do about this. Are there morally permissible/necessary ways of ensuring that there remain enough liberal-minded people to maintain liberal institutions, assuming, as sociologist Christian Joppke puts it bluntly, that ‘you cannot run a liberal state that is filled up to the ceiling with illiberal people’? This scholarly project is the first to provide an answer to this (understandably) sensitive question.