The rules under which jurisdictions (nations, provinces) can deny immigration or expel residents are generally governed by a constitution, but there do not exist either positive or normative analyses to suggest what types of exclusion rules are best. We stylise this problem by suggesting four constitutional rules of admission: free mobility, admission by majority vote, admission by unanimous consent, admission by a demand threshold for public goods. In a simple model we characterise the equilibria that result from these rules, and provide a positive theory for which constitutional rule will be chosen.