Both the Cook Islands and Niue are self-governing states in free association with New Zealand. The details of their free association arrangement are contained in several documents, such as their respective constitutions, the 1983 Exchange of Letters between the governments of New Zealand and the Cook Islands, and the 2001 Joint Centenary Declaration. As such, the New Zealand Parliament is not empowered to unilaterally pass legislation in respect of these states. In foreign affairs and defence issues New Zealand acts on behalf of these countries, but only with their advice and consent. They do not (currently) make claim to separate sovereignty.