Mato Grosso (Portuguese pronunciation: [ˈmatu ˈɡɾosu] ^ⓘ – lit. 'Thick Bush') is one of the states of Brazil, the third largest by area, located in the Central-West region. The state has 1.66% of the Brazilian population and is responsible for 1.9% of the Brazilian GDP. Neighboring states (from west clockwise) are: Rondônia, Amazonas, Pará, Tocantins, Goiás and Mato Grosso do Sul. It is divided into 142 municipalities and covers an area of 903,357 square kilometers, consequently the state is roughly 82.2% of the size of its southwest neighbor, the nation of Bolivia.

A state with a flat landscape that alternates between vast chapadas and plain areas, Mato Grosso contains three main ecosystems: the Cerrado, the Pantanal and the Amazon rainforest. The Chapada dos Guimarães National Park, with its caves, grottoes, tracks, and waterfalls, is one of its tourist attractions. The extreme northwest of the state has a small part of the Amazonian forest. The Xingu Indigenous Park and the Araguaia River are in Mato Grosso. Farther south, the Pantanal, the world's largest wetland, is the habitat for nearly one thousand species of animals and many aquatic birds.

The varied terrain of Mato Grosso includes cliffs, canyons, and waterfalls. It is home to the Chapada dos Guimarães National Park, its sandstone mountains have eroded into a remarkably varied vistas.

The biologically rich Pantanal, one of the world's largest wetland/prairie ecosystems, is also located within this state. The Paraguay basin is rich in the number and diversity of fish (around 230 species), a fascinating place for fishermen and scholars. In this basin are numerous species classified as "noble" in sport fishing, others, including ornamental species, are of great interest to aquarists and still others whose rarity has led to detailed research. The fishing industry in the Pantanal plays an important role in the region's economy and, for local people, fish is a staple food. The Pantanal has a habitat similar to the Everglades in Florida in the United States, although the Pantanal is much larger.

The Bororo Indians live in the Mato Grosso area. As late as 1880, soldiers patrolled lands on the outskirts of Cuiabá, Mato Grosso's capital and largest city, to protect settlers from Bororo raids.

By the end of the 19th century, although severely reduced by disease and by warfare with explorers, slave traders, prospectors, settlers, and other indigenous groups, as many as five to 10 thousand Bororo continued to occupy central and eastern Mato Grosso, as well as western Goiás. The southwestern part of this state was ceded by Brazil to Bolivia in exchange for the then-Bolivian territory of Acre, according to the Treaty of Petrópolis in 1903.

This historically remote area attracted expeditions of exploration in the early 20th century that sought to find lost civilizations. A notable example was British Captain Percy Fawcett's expedition to find the Lost City of Z which he believed existed in the jungles of Brazil. Certain proponents of the Hollow Earth hypothesis speculated that the region had sites of access to the interior of the earth and its settlements.

In 1977, the state was split into two halves, and the neighboring state of Mato Grosso do Sul was created from the other part of its territory.