The world is in the midst of a substantial urban transition, but the impacts of this on the environment and human societies are not fully understood. Very little attention has been paid to urbanization processes in developing countries with smaller populations, despite the evident problems associated with urbanization. There are both biophysical and social vulnerabilities associated with urbanization in the South Pacific andthese vulnerabilities affect human security. The biophysical vulnerabilities include the fragile environments of the island nations, limited land resources, shortages of basic resources, and the risks associated with global warming. The ability to respond to these problems is constrained by social vulnerabilities, notably weak economies, difficulties associated with land ownership, and institutional limitations. There is a need for institutional reform, improved planning, better urban resource management, and greater regional cooperation, if Pacific island nations are to respond effectively to rapid urbanization and global change.