Oregon is a state in the Pacific Northwest region of the United States. Oregon borders the Pacific Ocean on the west, Washington on the north, Idaho on the east, and California and Nevada on the south. The Columbia and Snake Rivers form, respectively, much of its northern and eastern borders. Between two north-south mountain ranges in western Oregon—the Oregon Coast Range and the Cascade Mountain Range—lies the Willamette Valley, the most densely populated and agriculturally productive region of the state.

Oregon has one of the most diverse landscapes of any state in the U.S. It is well known for its tall, dense forests; its accessible and scenic Pacific coastline; and its rugged, glaciated Cascade volcanoes. Other areas include semiarid scrublands, prairies, and deserts that cover approximately half the state in eastern and north-central Oregon.

Oregon's population in 2000 was about 3.5 million, a 20.3% increase over 1990. It is estimated to have reached 3.7 million by 2006.

The origin of the name "Oregon" is unknown. One account, advanced by George R. Stewart in a 1944 article in American Speech, was endorsed as the "most plausible explanation" in the book Oregon Geographic Names. According to Stewart, the name came from an engraver's error in a French map published in the early 1700s, on which the Ouisiconsink (Wisconsin) River was spelled "Ouaricon-sint," broken on two lines with the -sint below, so that there appeared to be a river flowing to the west named "Ouaricon." Other theories find the roots in the Spanish language, from words like Orejón ("big ear") or Aragón.

By the 16th century Oregon was home to many Native American tribes, including the Bannock, Chasta, Chinook, Kalapuya, Klamath, Molalla, Nez Perce, and Umpqua. James Cook explored the coast in 1778 in search of the Northwest Passage. The Lewis and Clark Expedition traveled through the region during their expedition to explore the Louisiana Purchase. They built their winter fort at Fort Clatsop, near the mouth of the Columbia River. Exploration by Lewis and Clark (1805–1806) and the United Kingdom's David Thompson (1811) publicized the abundance of fur-bearing animals in the area. In 1811, New York financier John Jacob Astor established Fort Astoria at the mouth of the Columbia River as a western outpost to his Pacific Fur Company. Fort Astoria was the first permanent white settlement in Oregon.

In the War of 1812, the British gained control of all of the Pacific Fur Company posts. By the 1820s and 1830s, their Hudson's Bay Company dominated the Pacific Northwest from its Columbia District headquarters at Fort Vancouver (built in 1825 by the District's Chief Factor John McLoughlin across the Columbia from present-day Portland).

In 1841, the master trapper and entrepreneur Ewing Young died with considerable wealth, with no apparent heir, and no system to probate his estate. A meeting followed Young's funeral at which a probate government was proposed. Doctor Ira L. Babcock of Jason Lee's Methodist Mission was elected Supreme Judge. Babcock chaired two meetings in 1842 at Champoeg (half way between Lee's mission and Oregon City) to discuss wolves and other animals of contemporary concern. These meetings were precursors to an all-citizen meeting in 1843, which instituted a provisional government headed by an executive committee made up of David Hill, Alanson Beers, and Joseph Gale. This government was the first acting public government of the Oregon Country before American annexation.

The Oregon Trail infused the region with new settlers, starting in 1842–1843, after the United States agreed to jointly settle the Oregon Country with the United Kingdom. The border was resolved in 1846 by the Oregon Treaty after a period during which it seemed that the United States and the United Kingdom would go to war for a third time in 75 years. Cooler heads prevailed, and the Oregon boundary dispute between the United States and British North America was set at the 49th parallel. The Oregon Territory was officially organized in 1848.

Settlement increased because of the Donation Land Claim Act of 1850, in conjunction with the forced relocation of the native population to Indian reservations in Oregon. The state was admitted to the Union on February 14, 1859.

At the outbreak of the American Civil War, regular U.S. troops were withdrawn and sent east. Volunteer cavalry were recruited in California and were sent north to Oregon to keep peace and protect the populace. The First Oregon Cavalry served until June 1865.

In the 1880s, the proliferation of railroads assisted in marketing of the state's lumber and wheat, as well as the more rapid growth of its cities.

Industrial expansion began in earnest following the construction of the Bonneville Dam in 1943 on the Columbia River. The power, food, and lumber provided by Oregon helped fuel the development of the West, although the periodic fluctuations in the nation's building industry have hurt the state's economy on multiple occasions.