Lower Rio Grande Valley in the context of Brownsville-Harlingen

The Rio Grande (/ˌriːoʊ ˈɡrænd/ or /ˌriːoʊ ˈɡrɑːndeɪ/) in the United States or the Río Bravo (del Norte) in Mexico (Spanish pronunciation: [ˈri.o ˈβɾaβo ðel ˈnoɾte]), also known as Tó Ba'áadi in Navajo, is one of the principal rivers (along with the Colorado River) in the Southwestern United States and in northern Mexico. The length of the Rio Grande is 1,896 miles (3,051 km), making it the 4th longest river in the United States and in North America by main stem. It originates in south-central Colorado, in the United States, and flows to the Gulf of Mexico. The Rio Grande drainage basin (watershed) has an area of 182,200 square miles (472,000 km); however, the endorheic basins that are adjacent to and within the greater drainage basin of the Rio Grande increase the total drainage-basin area to 336,000 square miles (870,000 km).

The Rio Grande with its fertile valley, along with its tributaries, is a vital water source for seven U.S. and Mexican states, and flows primarily through arid and semi-arid lands. After traversing the length of New Mexico, the Rio Grande becomes the Mexico–United States border, between the U.S. state of Texas and the northern Mexican states of Chihuahua and Coahuila, Nuevo León and Tamaulipas; a short segment of the Rio Grande is a partial state-boundary between the U.S. states of New Mexico and Texas. Since the mid–twentieth century, only 20 percent of the Rio Grande's water reaches the Gulf of Mexico, because of the voluminous consumption of water required to irrigate farmland (e.g. the Mesilla and Lower Rio Grande Valleys) and to continually hydrate cities (e.g. Albuquerque); such water usages are additional to the reservoirs of water retained with diversion dams. 260 miles (418 km) of the river in New Mexico and Texas are designated as the Rio Grande Wild and Scenic River.

South Texas is a geographic and cultural region of the U.S. state of Texas that lies roughly south of—and includes—San Antonio. The southern and western boundary is the Rio Grande, and to the east it is the Gulf of Mexico. The population of this region is more than 5 million according to the 2024 census estimates. The southern portion of this region is often referred to as the Rio Grande Valley. The eastern portion along the Gulf of Mexico is also referred to as the Coastal Bend.

Greater Houston and Beaumont–Port Arthur are occasionally tied to the region, both for physically being on the southern end of the state and for businesses that use "South Texas" in its name. (i.e. South Texas School of Law, South Texas State Fair, etc.). However, the two are more commonly associated with East Texas or Southeast Texas.

Brazos Island, also known as Brazos Santiago Island, is a barrier island on the Gulf Coast of Texas in the United States, south of the town of South Padre Island and north of the city of Starbase. The island is located in Cameron County.

Brazos Santiago Pass partitions the barrier islands of Brazos Island and Padre Island in the Lower Rio Grande Valley.

Texas's 15th congressional district of the United States House of Representatives includes a thin section of the far south of the state of Texas. The district's current Representative is Republican Monica De La Cruz. Elected in 2022, De La Cruz is the first Republican and woman to represent the district.

Currently, the 15th congressional district composes of a narrow strip of land running from western Hidalgo County in the Rio Grande Valley northwards to eastern Guadalupe County, to the east of San Antonio. The district includes the entirety of Brooks, Jim Wells, Live Oak, Karnes, and Wilson counties between Hidalgo and Guadalupe counties.

Matamoros–Brownsville, also known as Brownsville–Matamoros, or simply as the Borderplex, is one of the six transborder agglomerations along the Mexico–United States border. It is part of the Lower Rio Grande Valley region. The city of Matamoros is situated in the Mexican state of Tamaulipas, on the south bank of the Rio Grande, while the city of Brownsville is located in the U.S. state of Texas, directly north across the bank of the Rio Grande. The Matamoros–Brownsville area is connected by four international bridges. In addition, this transnational conurbation area has a population of 1,136,995, making it the fourth-largest metropolitan area on the Mexico-U.S. border.

The area of Matamoros–Brownsville lies among the top-10 fastest-growing urban areas in the United States. The Brownsville–Harlingen and the Brownsville–Harlingen–Raymondville metropolitan areas are included in the official countdown of this transnational conurbation.

Area code 956 is a telephone area code in the North American Numbering Plan for the Lower and Middle Rio Grande Valley regions in the U.S. state of Texas. The numbering plan area (NPA) includes the communities of Brownsville, McAllen, Laredo and South Padre Island. The area code was created on May 25, 1997, in a split of NPA 210.

Projections in 2024 by the North American Numbering Plan Administrator (NANPA) indicated that 956 will enter exhaustion levels by late 2027 and relief action will be required in the Rio Grande Valley by that time.