This article investigates what moral principles should inform states' decisions to grant resident migrants the rights of full citizenship. Some work on this question has focused on the beliefs and attitudes it is thought desirable for migrants to have. This article takes a different approach. Beginning from the assumption that a high rate of naturalisation is desirable, the article investigates four arguments in its favour. The contribution argument says that residents merit citizenship by virtue of their productive contribution to their new society. The coercion argument says it is wrong to impose on resident migrants laws they had no say in making. The membership argument says that migrants merit citizenship because they are already membe...