Micronesia (UK: , US: ) is a subregion of Oceania, consisting of approximately 2,000 small islands in the Northwestern Pacific Ocean. It has a close shared cultural history with three other island regions: Maritime Southeast Asia to the west, Polynesia to the east, and Melanesia to the south—as well as with the wider community of Austronesian peoples.

The region has a tropical marine climate and is part of the Oceanian realm. It includes four main archipelagos—the Caroline Islands, the Gilbert Islands, the Mariana Islands, and the Marshall Islands — as well as numerous islands that are not part of any archipelago.

Political control of areas within Micronesia varies depending on the island, and is distributed among six sovereign nations. Some of the Caroline Islands are part of the Republic of Palau and some are part of the Federated States of Micronesia (often shortened to "FSM" or "Micronesia"—not to be confused with the identical name for the overall region). The Gilbert Islands (along with the Phoenix Islands and the Line Islands in Polynesia) comprise the Republic of Kiribati. The Mariana Islands are affiliated with the United States; some of them belong to the U.S. Territory of Guam and the rest belong to the U.S. Commonwealth of the Northern Mariana Islands. The island of Nauru is its own sovereign nation. The Marshall Islands all belong to the Republic of the Marshall Islands. The sovereignty of Wake Island is contested: it is claimed both by the United States and by the Republic of the Marshall Islands. The United States has actual possession of Wake Island, which is under the immediate administration of the United States Air Force.

Notwithstanding the fact that the notion of "Micronesia" has been quite well established since 1832 and has been used ever since, by most popular works, this set does not correspond to any geomorphological, archaeological, linguistic, ethnic or cultural unity, but on the contrary represents a disparate ensemble, with no real deep unity. In fact, "Micronesian people" does not exist as a subset of the sea-migrating Austronesian people, who may also include the Polynesian people and the hypothetical Australo-Melanesian or "Melanesian people".

Human settlement of Micronesia began several millennia ago. Based on the current scientific consensus, the Austronesian peoples originated from a prehistoric seaborne migration, known as the Austronesian expansion, from pre-Han Formosa, at around 3000 to 1500 BCE. Austronesians reached the northernmost Philippines, specifically the Batanes Islands, by around 2200 BCE. Austronesians were the first people to invent oceangoing sailing technologies (notably catamarans, outrigger boats, lashed-lug boat building, and the crab claw sail), which enabled their rapid dispersal into the islands of the Indo-Pacific. From 2000 BCE they assimilated (or were assimilated by) the earlier populations on the islands in their migration pathway.

The earliest known contact of Europeans with Micronesia was in 1521, when Magellan expedition landed in the Marianas. Jules Dumont d'Urville is usually credited with coining the term "Micronesia" in 1832, but in fact, Louis Domeny de Rienzi used this term a year earlier.