Houston is the most populous city in the U.S. state of Texas and the Southern United States. It is the fourth-most populous city in the United States, with a population of 2.3 million at the 2020 census. The Greater Houston metropolitan area, at 7.8 million residents, is the fifth-most populous metropolitan area in the nation and second-most populous in Texas. Located in Southeast Texas near Galveston Bay and the Gulf of Mexico, Houston is the seat of Harris County. Covering a total area of 640.4 square miles (1,659 km²), it is the ninth largest city in the country and the largest whose municipal government is not consolidated with a county, parish, or borough. Although primarily located within Harris County, portions of the city extend into Fort Bend and Montgomery counties. Houston also functions as the southeastern anchor of the Texas Triangle megaregion.

Houston was founded by land investors on August 30, 1836, at the confluence of Buffalo Bayou and White Oak Bayou (a point now known as Allen's Landing) and incorporated as a city on June 5, 1837. The city is named after former General Sam Houston, who was president of the Republic of Texas and had won Texas's independence from Mexico at the Battle of San Jacinto 25 miles (40 km) east of Allen's Landing. After briefly serving as the capital of the Texas Republic in the late 1830s, Houston grew steadily into a regional trading center for the remainder of the 19th century. The 20th century brought a convergence of economic factors that fueled rapid growth in Houston, including a burgeoning port and railroad industry, the decline of Galveston as Texas's primary port following a devastating 1900 hurricane, the subsequent construction of the Houston Ship Channel, and the Texas oil boom. In the mid-20th century, Houston's economy diversified, as it became home to the Texas Medical Center—the world's largest concentration of healthcare and research institutions—and NASA's Johnson Space Center, home to the Mission Control Center.

Since the late 19th century, Houston's economy has had a broad industrial base in energy, manufacturing, aeronautics, and transportation. Leading in healthcare sectors and building oilfield equipment, Houston has the second-most Fortune 500 headquarters of any U.S. municipality within its city limits. The Port of Houston ranks first in the United States in international waterborne tonnage handled and second in total cargo tonnage handled.

Nicknamed the "Bayou City", "Space City", "H-Town", and "the 713", Houston has become a global city, with strengths in culture, medicine, and research. The city's population comprises various ethnic and religious backgrounds, as well as a large and growing international community. Houston is the most diverse metropolitan area in Texas and has been described as the most racially and ethnically diverse major city in the U.S. It is home to many cultural institutions and exhibits, such as the Houston Museum District and the Houston Theater District.

Present-day Houston sits on land that was once occupied by the Karankawa and the Atakapa indigenous peoples for at least 2,000 years before the first known settlers arrived. These tribes are almost nonexistent today; this was most likely caused by foreign disease, and competition with various settler groups in the 18th and 19th centuries. However, the land then remained largely uninhabited from the late 1700s until settlement in the 1830s.

The Allen brothers—Augustus Chapman and John Kirby—explored town sites on Buffalo Bayou and Galveston Bay. According to historian David McComb, "[T]he brothers, on August 26, 1836, bought from Elizabeth E. Parrott, wife of T.F.L. Parrott and widow of John Austin, the south half of the lower league [2,214-acre (896 ha) tract] granted to her by her late husband. They paid $5,000 total, but only $1,000 of this in cash; notes made up the remainder."

The Allen brothers ran their first advertisement for Houston just four days later in the Telegraph and Texas Register, naming the notional town in honor of Sam Houston, who would become President later that year. They successfully lobbied the Republic of Texas Congress to designate Houston as the temporary capital, agreeing to provide the new government with a state capitol building. About a dozen persons resided in the town at the beginning of 1837, but that number grew to about 1,500 by the time the Texas Congress convened in Houston for the first time that May. The Republic of Texas granted Houston incorporation on June 5, 1837, as James S. Holman became its first mayor. In the same year, Houston became the county seat of Harrisburg County (now Harris County).

In 1839, the Republic of Texas relocated its capital to Austin. The town suffered another setback that year when a yellow fever epidemic claimed about one life for every eight residents, yet it persisted as a commercial center, forming a symbiosis with its Gulf Coast port, Galveston. Landlocked farmers brought their produce to Houston, using Buffalo Bayou to gain access to Galveston and the Gulf of Mexico. Houston merchants profited from selling staples to farmers and shipping the farmers' produce to Galveston.