We review the international and New Zealand literatures on the two-way interaction between international migration and agreements designed to enhance cross-border trade or investment. Benefits and costs of migration, to the extent that these may feature in trade and migration negotiations, are discussed. While trade and migration can be substitutes in some contexts, they will be complements in other contexts. Liberalisation of services and the movement of people are likely to offer much more significant gains than liberalisation of remaining barriers to goods trade. Significant scope for liberalisation under GATS mode 4 (the movement of natural persons) may remain. However, temporary migration is already promoted on a unilateral and bilateral basis within immigration policy frameworks that may provide greater flexibility than GATS mode 4. With respect to both trade and migration, the more diverse the exchanging countries are, the greater the economic benefits tend to be. However, greater diversity may also imply greater social costs. This paradox of diversity needs to be addressed through appropriate social policies accompanying enhanced temporary and permanent migration.