Missouri ( mih-ZOOR-ee) is a state in the Midwestern region of the United States. Ranking 21st in land area, it borders Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas to the south and Oklahoma, Kansas, and Nebraska to the west. In the south are the Ozarks, a forested highland, providing timber, minerals, and recreation. At 1.5 billion years old, the St. Francois Mountains are among the oldest in the world. The Missouri River, after which the state is named, flows through the center and into the Mississippi River, which makes up the eastern border. With over six million residents, it is the 18th-most populous state of the country. The largest urban areas are St. Louis, Kansas City, Springfield, and Columbia. The capital is Jefferson City.

Humans have inhabited present-day Missouri for at least 12,000 years. The Mississippian culture, which emerged in the ninth century, built cities and mounds before declining in the 14th century. The Indigenous Osage and Missouria nations inhabited the area when European people arrived in the 17th century. The French incorporated the territory into Louisiana, founding Ste. Genevieve in 1735 and St. Louis in 1764. After a brief period of Spanish rule, the United States acquired Missouri as part of the Louisiana Purchase in 1803. Americans from the Upland South rushed into the new Missouri Territory; Missouri played a central role in the westward expansion of the United States. Missouri was admitted as a slave state as part of the Missouri Compromise of 1820. As a border state, Missouri's role in the American Civil War was complex, and it was subject to rival governments, raids, and guerilla warfare. After the war, both Greater St. Louis and the Kansas City metropolitan area became large centers of industrialization and business.

Today the state is divided into 114 counties and the independent city of St. Louis. Missouri has been called the "Mother of the West", the "Cave State", and the "Show Me State". Its culture blends elements of the Midwestern and Southern United States. It is the birthplace of the musical genres ragtime, Kansas City jazz and St. Louis blues. The well-known Kansas City-style barbecue, and the lesser-known St. Louis-style barbecue, can be found across the state and beyond.

Missouri is a major center of beer brewing and has some of the most permissive alcohol laws in the U.S. It is home to Anheuser-Busch, the world's largest beer producer, and produces Missouri wine, especially in the Missouri Rhineland. Outside the state's major cities, popular tourist destinations include the Lake of the Ozarks, Table Rock Lake and Branson. Some of the largest companies based in the state include Cerner, Express Scripts, Monsanto, Emerson Electric, Edward Jones, H&R Block, Wells Fargo Advisors, Centene Corporation, and O'Reilly Auto Parts. Well-known universities in Missouri include the University of Missouri, Saint Louis University, and Washington University in St. Louis.