Micronesia ((UK: , US: ); from Greek: μικρός mikrós "small" and Greek: νῆσος nêsos "island") is a subregion of Oceania, composed of thousands of small islands in the western Pacific Ocean. It has a shared cultural history with two other island regions, Polynesia to the east and Melanesia to the south.
The region has a tropical marine climate, and is part of the Oceania ecozone. There are four main archipelagos along with numerous outlying islands.
Micronesia is divided politically among several sovereign countries. One of these is the Federated States of Micronesia, which is often called "Micronesia" for short and is not to be confused with the overall region. The Micronesia region encompasses five sovereign, independent nations—the Federated States of Micronesia, Palau, Kiribati, Marshall Islands, and Nauru—as well as three U.S. territories in the northern part: Northern Mariana Islands, Guam, and Wake Island.
Micronesia began to be settled several millennia ago, although there are competing theories about the origin and arrival of the first settlers. The earliest known contact with Europeans occurred in 1521, when Ferdinand Magellan reached the Marianas. The coinage of the term "Micronesia" is usually attributed to Jules Dumont d'Urville's usage in 1832; however, Domeny de Rienzi had used the term a year previously.