Map - Matamoros, Tamaulipas (Heroica Matamoros)

Matamoros, officially known as Heroica Matamoros, is a city in the northeastern Mexican state of Tamaulipas, and the municipal seat of the homonymous municipality. It is on the southern bank of the Rio Grande, directly across the border from Brownsville, Texas, United States. Matamoros is the second largest city in the state of Tamaulipas. As of 2016, Matamoros had a population of 520,367. In addition, the Matamoros–Brownsville Metropolitan Area has a population of 1,387,985, making it the 4th largest metropolitan area on the Mexico–US border. Matamoros is the 39th largest city in Mexico and anchors the second largest metropolitan area in Tamaulipas.

The economy of the city is significantly based on its international trade with the United States through the USMCA agreement, and it is home to one of the most promising industrial sectors in Mexico, mainly due to the presence of maquiladoras. In Matamoros, the automotive industry hosts the assembly and accessories plants for brands such as General Motors, Ford, Chrysler, BMW, and Mercedes Benz. Prior to the growth of the maquiladoras in the 2000s, Matamoros' economy had historically been principally based on agriculture, since northern Mexico's biggest irrigation zones are in the municipality. PEMEX announced a multibillion-peso offshore drilling project for the port of Matamoros, one of the future prospects for Mexico's oil industry.

Matamoros is a major historical site, the site of several battles and events of the Mexican War of Independence, the Mexican Revolution, the Texas Revolution, the Mexican–American War, the American Civil War, and the French Intervention that allowed the city to earn its title of "Undefeated, Loyal, and Heroic". The Mexican National Anthem was played for the first time in public at an opera house, the Teatro de la Reforma (sometimes known as The Opera Theater) in Matamoros.

Matamoros has a semiarid climate, with mild winters and hot, humid summers. Matamoros and Brownsville, Texas, are home to the Charro Days and Sombrero Festival, two-nation fiestas that commemorate the heritage of the U.S. and Mexico which are celebrated every February.