Texas is a state located in the southern and southwestern regions of the United States of America. With an area of 261,797 square miles (678,051 km²) and a population of 23,507,783 (based on a 2006 U.S. census bureau estimate) in 254 counties, the state is second-largest in both area (behind Alaska) and population (behind California). About half the state's population resides in either the Dallas–Fort Worth or Houston metropolitan areas.

The state's name a word in the Caddoan language of the Hasinai, which means "friends" or "allies." Texas declared its independence from Mexico in 1836 and existed as the independent Republic of Texas for nearly a decade. In 1845, it joined the United States as the 28th state.

Texas is internationally known for its energy and aeronautics industries, and for the ship channel at the Port of Houston—the largest in the U.S. in international commerce and the sixth-largest port in the world. The state is home to the most Fortune 500 companies in the United States and has the second-largest economy in the United States, behind California. The Texas Medical Center in Houston contains the world's largest concentration of research and healthcare institutions.

In addition to its own state flag, Texas boasts that "Six Flags" have flown over its soil: the national flags of Spain, the Fleur-de-lis of France, Mexico, the Republic of Texas, the Confederate States of America, and the United States of America.

American Indian tribes who once lived inside the boundaries of present-day Texas include Apache, Atakapan, Bidai, Caddo, Comanche, Cherokee, Kiowa, Tonkawa, Wichita, Hueco and the Karankawa of Galveston. Currently, there are three federally recognized Native American tribes which reside in Texas: the Alabama-Coushatta Tribe of Texas, the Kickapoo Traditional Tribe of Texas, and the Ysleta Del Sur Pueblo of Texas.

On 6 November 1528, shipwrecked Spanish conquistador Álvar Núñez Cabeza de Vaca became the first known European in Texas. Most of Texas was immediately claimed by Spain as part of the Spanish dominions of New Spain. However, France took advantage of Spain's failure to settle the land and in 1685 established Fort St. Louis and claimed most of Texas. The first Spanish colonization did not come until a few years after Fort St. Louis, as Spain was spurred by France to enforce its claims. The French claim was inherited by the United States as they bought the Louisiana Purchase in 1803 and the Spanish claim was later inherited by Mexico during the Mexican War of Independence of 1821, setting the stage for the Mexican–American War. The French settlement was massacred by American Indians, and Spain only started sparse settlements, so most permanent settlements by Europeans didn't start until long after the first explorer arrived in 1521.

In the 1800s, two main ethnic groups settled the land: Tejanos and eventually Anglo Americans. By 1830, the 30,000 Anglo settlers in Texas outnumbered the Tejanos two to one. Smaller numbers of Europeans also came. Moses Austin bought 200,000 acres (810 km²) of land of his choice, and moved to San Antonio in August of 1821. His son, Stephen F. Austin, joined him. In 1821, Texas became part of the newly independent Republic of Mexico and, in 1824, became the northern section of Coahuila y Tejas. On 3 January 1823, Stephen F. Austin began a colony of 300 Anglo American families known as the "Old Three Hundred" along the Brazos River, after Austin was authorized to do so by Governor Antonio María Martínez and then successive Mexican officials as Mexico went through tumultuous political regime changes. Austin soon organized even more groups of immigrants, with authorization from the Mexican government. Meanwhile, more Tejanos were also settling in Texas, and as Antonio Menchaca writes in "Memoirs" in 1907, many Tejanos were already desirous of joining the United States. Tejanos were mostly full-blooded Spanish immigrants, few partly or entirely of American Indian heritage as most Mexicans south of the Rio Grande were.

The "Conventions" of 1832 and 1833 were a response to rising unrest at the policies of the ruling Mexican government, which included the end of duty free imports from the United States and the potential end to the special allowance for slavery in the state. Slavery had been abolished in Mexico with the independence. Spain's policy of allowing only full-blooded Spaniards to settle Texas also ended with independence. In 1835, Antonio López de Santa Anna, President of Mexico, proclaimed a unified constitution for all Mexican territories, including Texas. The new Constitution ended the republic and the federation, imposed a central style of government with power concentrated in the President, and turned states into provinces with governors appointed from Mexico City. Some states around Mexico rebelled against this imposition, including Chihuahua, Zacatecas and Yucatan. Texans were also irritated by other policies including the forcible disarmament of Texan settlers, and the expulsion of immigrants and legal land owners originally from the United States. The example of the Centralista forces' suppression of dissidents in Zacatecas also inspired fear of the Mexican government.

On 2 March 1836, the Convention of 1836 signed a Declaration of Independence, declaring Texas an independent nation. On 21 April 1836, the Texans—led by General Sam Houston—won their independence when they defeated the Mexican forces of Santa Anna at the Battle of San Jacinto. Santa Anna was captured and signed the Treaties of Velasco, which gave Texas firm boundaries; Mexico repudiated the treaties, considered Texas a breakaway province, and vowed to reconquer it. Later in 1836, the Texans adopted a constitution that formally legalized slavery in Texas. The Republic of Texas included the area of the present state of Texas, and additional unoccupied territory to the west and northwest.

Texans wanted annexation to the United States. Texas was fast-growing, but still poor and had great difficulty maintaining self-defense. Events such as the Dawson Massacre and two recaptures of Béxar in Texas of 1842 helped add momentum to the desire for statehood. However, American politics intruded; strong Northern opposition to adding another slave state blocked annexation until the election of 1844 was won on a pro-annexation platform by James K. Polk. On 29 December 1845, Texas was admitted to the U.S. as a constituent state of the Union. The Mexican–American War followed, with decisive American victories. Soon after, Texas grew rapidly as migrants poured into the cotton lands.

Just prior to the American Civil War, elected delegates met in convention and, in an act whose legality was later upheld by the Texas Legislature, authorized secession from the U.S. on 1 February 1861 by a thundering majority. Texas voters later overwhelmingly approved the measure in referendum, and the state was accepted as a charter member by the provisional government of the Confederate States of America on 1 March 1861. Partly due to its distance from the front lines of the war, a major role for Texas was to supply hardy soldiers for Confederate forces (veterans of the Mexican–American War), especially in cavalry. Although Texan regiments fought in every major battle throughout the war, Texas was largely considered a "supply state" for the Confederate forces until mid-1863, when the Union capture of the Mississippi River made large movements of men or cattle impossible. The last battle of the Civil War was fought in Texas, at Palmito Ranch, on 12 May 1865, well after Lee's surrender on 9 April 1865 at Appomattox Court House in Virginia.

Texas descended into near-anarchy during the two months between the surrender of the Army of Northern Virginia and the assumption of authority by Union General Gordon Granger, as Confederate forces demobilized or disbanded and government property passed into private hands through distribution or plunder. June 10th commemorates the announcement of the Emancipation Proclamation on 19 June 1865 in Galveston by General Gordon Granger; nearly 1-1/2 years after the original announcement of 1 January 1863. On 30 March 1870, although Texas did not meet all the requirements, the United States Congress readmitted Texas into the Union.

The first major oil well in Texas was drilled at Spindletop, a little hill south of Beaumont, on the morning of 10 January 1901. Other oil fields were later discovered nearby in East Texas, West Texas, and under the Gulf of Mexico. The resulting "Oil Boom" permanently transformed the economy of Texas. Oil production eventually averaged three million barrels of oil per day at its peak in 1972. The economy, which had experienced significant recovery since the American Civil War, was dealt a double blow by the Great Depression and the Dust Bowl.

From 1950 through the 1960s, Texas modernized and dramatically expanded its system of higher education. Under the leadership of Governor John B. Connally, the state produced a long-range plan for higher education, a more rational distribution of resources, and a central state apparatus designed to manage state institutions more efficiently. Because of these changes, Texas universities received federal funds for research and development during the Kennedy and Johnson administrations.