The document discusses the three main regions of the Pacific Islands - Melanesia, Micronesia, and Polynesia. Melanesia consists of the islands closest to Australia and includes the most populated islands, many of which are high volcanically formed islands. Micronesia lies north of the equator and contains low islands and atolls, with many less than 1 square mile in size. Polynesia is the largest region, including Hawaii, and mostly contains high, densely forested islands.