Oaxaca, officially the Free and Sovereign State of Oaxaca, is one of the 32 states that compose the Federative Entities of the United Mexican States. It is divided into 570 municipalities, of which 418 (almost three quarters) are governed by the system of usos y costumbres (customs and traditions) with recognized local forms of self-governance. Its capital city is Oaxaca de Juárez.

Oaxaca is in southern Mexico. It is bordered by the states of Guerrero to the west, Puebla to the northwest, Veracruz to the north, and Chiapas to the east. To the south, Oaxaca has a significant coastline on the Pacific Ocean.

The state is best known for its Indigenous peoples and cultures. The most numerous and best known are the Zapotecs and the Mixtecs, but 16 are officially recognized. These cultures have survived better than most others in Mexico due to the state's rugged and isolating terrain. Most live in the Central Valleys region, which is also an economically important area for tourism, with people attracted for its archeological sites such as Monte Albán, and Mitla, and its various native cultures and crafts. Another important tourist area is the coast, which has the major resort of Huatulco and sandy beaches of Puerto Escondido, Puerto Ángel, Zipolite, Bahia de Tembo, and Mazunte. Oaxaca is also one of Mexico's most biologically diverse states, ranking in the top three, along with Chiapas and Veracruz, for numbers of reptiles, amphibians, mammals and plants.

The name of the state comes from the name of its capital city, Oaxaca. This name comes from the Nahuatl word "Huaxyacac", which refers to a tree called a "guaje" (Leucaena leucocephala) found around the capital city. The name was originally applied to the Valley of Oaxaca by Nahuatl-speaking Aztecs and passed on to the Spanish during the conquest of the Oaxaca region. The modern state was created in 1824, and the state seal was designed by Alfredo Canseco Feraud and approved by the government of Eduardo Vasconcelos. "Huaxyacac" [waːʃ.ˈja.kak] was transliterated as "Oaxaca" using Medieval Spanish orthography, in which the x represented the voiceless postalveolar fricative ([ʃ], the equivalent of English sh in "shop"), making "Oaxaca" pronounced as [waˈʃaka]. But during the 16th century the voiceless fricative sound evolved into a voiceless velar fricative ([x], like the ch in Scottish "loch"), and Oaxaca began to be pronounced [waˈxaka]. In present-day Spanish, Oaxaca is pronounced [waˈxaka] or [waˈhaka], the latter pronunciation used mostly in dialects of southern Mexico, the Caribbean, much of Central America, some places in South America, and the Canary Islands and western Andalusia in Spain, where [x] has become a voiceless glottal fricative ([h]).

Most of what is known about prehistoric Oaxaca comes from work in the Central Valleys region. Evidence of human habitation dating to about 11,000 years BCE has been found in the Guilá Naquitz cave near the town of Mitla. This area was recognized as a UNESCO World Heritage site in 2010 in recognition of the "earliest known evidence of domesticated plants in the continent, while corn cob fragments from the same cave are said to be the earliest documented evidence for the domestication of maize." More finds of nomadic peoples date to about 5000 BCE, with some evidence of the beginning of agriculture. By 2000 BCE, agriculture had been established in the Central Valleys region of the state, with sedentary villages. The diet developed around this time remained until the Spanish Conquest, consisting primarily of harvested corn, beans, chocolate, tomatoes, chili peppers, squash and gourds. Meat was generally hunted and included tepescuintle, turkey, deer, peccary, armadillo and iguana.

The oldest known major settlements, such as Yanhuitlán and Laguna Zope, are also in this area. The latter settlement is known for its small figures called "pretty women" or "baby face." Between 1200 and 900 BCE, pottery was produced in the area. This pottery has been linked with similar work done in La Victoria, Guatemala. Other important settlements from the same period include Tierras Largas, San José Mogote and Guadalupe, whose ceramics show Olmec influence. The major native language family, Oto-Manguean, is thought to have been spoken in northern Oaxaca around 4400 BCE and to have evolved into nine distinct branches by 1500 BCE.

Historic events in Oaxaca as far back as the 12th century are described in pictographic codices painted by Zapotecs and Mixtecs in the beginning of the colonial period, but outside of the information that can be obtained through their study, little historical information from pre-colonial Oaxaca exists, and our knowledge of this period relies largely on archaeological remains. By 500 BCE, Oaxaca's central valleys were mostly inhabited by the Zapotecs, with the Mixtecs on the western side. These two groups were often in conflict during the pre-Hispanic period. Archeological evidence indicates that between 750 and 1521, there may have been population peaks of as high as 2.5 million.

The Zapotecs were the earliest to gain dominance over the Central Valleys region. The first major dominion was centered in Monte Albán, which flourished from 500 BCE to AD 750. At its height, Monte Albán was home to 25,000 people and the capital city of the Zapotec nation. It remained a secondary center of power for the Zapotecs until the Mixtecs overran it in 1325. The site has several notable features, including the Danzantes, a set of stone reliefs, and the finding of fine quality ceramics.