Arkansas (IPA: /ˈɑɹkn̩ˌsɑː/) (are-can-saw) is a state located in the southern region of the United States of America. Arkansas shares a border with six states, with its eastern border largely defined by the Mississippi River. Its diverse geography ranges from the mountainous regions of the Ozarks and the Ouachita Mountains, which make up the U.S. Interior Highlands, to the eastern lowlands along the Mississippi River. The capital and most populous city is Little Rock, located in the central portion of the state.

The name Arkansas derives from the same root as the name for the State of Kansas. The Kansas tribe of American Indians are closely associated with the Sioux tribes. The word is a French pronunciation of a Quapaw (a related "Kaw" tribe) word meaning "land of downriver people" or "people of the south wind". The pronunciation of Arkansas (ar-kan-saw) was made official by an act of the state legislature in 1881 after a dispute between the two U.S. Senators from Arkansas. One wanted to pronounce the word ar-kan-sas and the other wanted ar-kan-saw.

With the exception of Hawaii, Arkansas is the smallest state entirely west of the Mississippi River. The Mississippi River forms most of Arkansas's eastern border, except in Clay and Greene counties where the St. Francis River forms the western boundary of the Missouri Bootheel, and in dozens of places where the current channel of the Mississippi has meandered from where it had last been legally specified.^[3] Arkansas shares its southern border with Louisiana, its northern border with Missouri, its eastern border with Tennessee and Mississippi, and its western border with Texas and Oklahoma.

Arkansas is a land of mountains and valleys, thick forests and fertile plains. Northwest Arkansas is part of the Ozark Plateau including the Boston Mountains, to the south are the Ouachita Mountains and these regions are divided by the Arkansas River; the southern and eastern parts of Arkansas are called the Lowlands. All of these mountains ranges are part of the U.S. Interior Highlands region, the only major mountainous region between the Rocky Mountains and the Appalachian Mountains.^[4][5] The highest point in the state is Mount Magazine in the Ouachita Mountains; it rises to 2,753 feet above sea level.

The so-called Lowlands are better known by names of their two regions, the Delta and the Grand Prairie. The Arkansas Delta is a flat landscape of rich alluvial soils formed by repeated flooding of the adjacent Mississippi. Further away from the river, in the southeast portion of the state, the Grand Prairie consists of a more undulating landscape. Both are fertile agricultural areas.

The Delta region is bisected by an unusual geological formation known as Crowley's Ridge. A narrow band of rolling hills, Crowley's Ridge rises from 250 to 500 feet above the surrounding alluvial plain and underlies many of the major towns of eastern Arkansas.

Arkansas is home to many caves, such as Blanchard Springs Caverns. It is also the first U.S. state in which diamonds were found (near Murfreesboro).