The Pacific Islands comprise 20,000 to 30,000 islands in the Pacific Ocean. The islands are also sometimes collectively called Oceania, although Oceania is sometimes defined as also including Australasia and the Malay Archipelago.

The Pacific Islands lying south of the tropic of Cancer are traditionally grouped into the three divisions of Melanesia, Micronesia, and Polynesia:

The region's islands are classified into two groups, high islands and low islands. Volcanoes form high islands, which generally can support more people and have a more fertile soil. Low islands are reefs or atolls, and are relatively small and infertile. Melanesia, the most populous of the three regions, contains mainly high islands, while most of Micronesia and Polynesia are low islands. In addition, there are many other islands located within the boundaries of the Pacific Ocean that are not considered part of Oceania. These islands include the Galápagos Islands of Ecuador; the Aleutian Islands in Alaska, United States; the Russian islands of Sakhalin and Kuril Islands; Taiwan and other islands of the Republic of China; the Philippines; islands in the South China Sea, which includes the disputed South China Sea Islands; most of the islands of Indonesia; and the island nation of Japan, which comprises the Japanese Archipelago.