The Marshalls were administered by the United States as part of the Trust Territory of the Pacific Islands (Pacific Islands, Trust Territory of the) from 1947 to 1986, when the Trust Territory was dissolved by the U.S. government.

The climate is tropical, with a mean annual temperature for the entire group of 82° F (28° C). Annual rainfall varies from 20 to 30 inches (500 to 800 millimetres) in the north to 160 inches in the southern atolls. The wettest months are October and November. Several of the northern atolls are uninhabited owing to insufficient rainfall. Most of the Marshall Islands are true atolls, consisting of an irregular, oval-shaped coral reef surrounding a lagoon; the islets lie along the coral reef. The islands and islets of the Ratak chain tend to be more heavily wooded than those of the Ralik. Coconut and pandanus palms and breadfruit trees are the principal vegetation. Soils are generally sandy and low in fertility.

The native people of the Marshalls (Marshall Islands) are Micronesians. The most populous atolls are Majuro and Kwajalein, which offers employment at the U.S. missile testing range; together they have more than two-thirds of the country's total population. The remaining one-third of the population lives in traditional villages on the outer islands away from the two urban centres. The American missionary effort began in the Marshalls in the 1850s and was exceedingly successful. The Marshallese today are predominantly Christian. The Marshallese and English languages are spoken, but only a minority are fluent in the latter.

Substantial U.S. subsidies to the Republic of the Marshall Islands under the Compact of Free Association (see below) and the leasing of land for the U.S. missile testing range on Kwajalein are the main sources of revenue for the nation. Employment and modern amenities at both Majuro and Kwajalein serve as magnets that draw people to the two urban centres.

On the outer islands, subsistence farming, fishing, and the raising of pigs and poultry are the principal economic activities. Coconut, pandanus, breadfruit, and taro are the major food crops. The production of copra is the chief source of income for the outer islands. The principal import is processed foods. Other major imports include machinery and transport equipment, manufactured goods, and fuels, primarily from the United States, Japan, and Australia.

Transportation among the atolls and islands is by boat or air. Government-owned ships make scheduled trips among the islands. Several commercial cargo lines also serve the islands. Majuro has a commercial dock complex, and many of the atolls have good anchorage within their lagoons. Majuro and Kwajalein have international airports, and domestic and regional flights link some of the other atolls and islands.

Under the constitution adopted in 1979, the government consists of a president elected by a unicameral, 33-member parliament known as the Nitijela. The Council of Iroji (Chiefs) has mainly a consultative function, concerned with traditional laws and customs.

A hospital on Majuro, a small sub-hospital on Ebeye island (part of Kwajalein Atoll), and dispensaries on other islands provide health care. There are primary schools, both public and church-run, on the inhabited islands and islets. Majuro and Jaluit atolls each have a public secondary school. Majuro is also the site of a centre for continuing education operated by the Federated States of Micronesia's College of Micronesia.

The Marshall Islands were settled initially around the beginning of the Christian Era by Micronesians who may have been influenced by early Polynesian (Lapita) culture. Radiocarbon dates from earth-oven charcoal samples that were excavated in Laura village on Majuro yielded dates of about 30 BC and AD 50. The early Marshall Islanders were skilled navigators and made long canoe voyages among the atolls.

Sighted in 1529 by the Spanish navigator Álvaro Saavedra, the Marshalls lacked the wealth to encourage exploitation or mapping. The British captain Samuel Wallis chanced upon Rongerik and Rongelap atolls while sailing from Tahiti to Tinian. The British naval captains John Marshall and Thomas Gilbert partially explored the Marshalls in 1788, but much of the mapping was done by Russian expeditions under Adam Johann Krusenstern (Krusenstern, Adam Johann) (1803) and Otto von Kotzebue (Kotzebue, Otto von) (1815 and 1823). U.S. whalers frequented the islands from the 1820s, and U.S. and Hawaiian Protestant missionaries (mission) began efforts to convert the islanders in the 1850s. Germany established a coaling station on Jaluit Atoll by treaty with island chiefs and in 1886, by agreement with Great Britain, established a protectorate over the Marshalls. Japan seized the islands in 1914 and later (after 1919) administered them as a League of Nations mandate. Occupied by the United States in World War II, following heavy fighting at Kwajalein and Enewetak, the Marshall Islands were made part of the United Nations Trust Territory of the Pacific Islands under jurisdiction of the United States in 1947. After their populations were removed to other atolls, Bikini and Enewetak served as an official testing ground for U.S. nuclear bombs (1946–58). The tests stopped in 1958 and cleanup efforts began in the late 1960s. During the trial resettlement of the Bikinians, however, their atoll was found to be too contaminated for permanent habitation, and by the late 1970s the people had to be evacuated once again. The Enewetak people were returned to their homeland, and a program to monitor Bikini was put in place.

After voting to separate from the other entities of the Trust Territory of the Pacific Islands, in 1978, the Marshall Islands drew up a constitution that voters approved in 1979. It formed the republic and brought internal self-government. In 1982 the government signed the Compact of Free Association with the United States. This agreement, approved by the voters in 1983, requires that the United States remain responsible for defense and external security and that it provide financial assistance for the republic. The compact entitles the United States to use the missile testing range on Kwajalein Atoll, and provides for the republic to become fully independent and to alter its status with the United States at any time, subject to approval of the residents through plebiscites. In 1983 the islanders reopened negotiations on the compact's provision regarding compensation for the people of the four atolls affected by the U.S. nuclear tests. The United States agreed to set up a separate fund for the people of the four atolls and established an open-ended fund to cover personal injury claims among the islanders; it also agreed to set up a joint U.S.-Marshallese claims tribunal. A further agreement set up a fund to improve living conditions on Ebeye island, where all Micronesians working on the Kwajalein missile range and base resided. The Trust Territory was dissolved in 1990 with the approval of the UN Security Council, and on Sept. 17, 1991, the Marshall Islands became a member of the UN.