The Bajío (the Lowlands) is a cultural and geographical region within the central Mexican plateau which roughly spans from northwest of Mexico City to the main silver mines in the northern-central part of the country. This includes (from south to north) the states of Querétaro, Guanajuato, parts of Jalisco (Centro, Los Altos de Jalisco), Aguascalientes and parts of Zacatecas, San Luis Potosí and Michoacán.

Located at the border between Mesoamerica and Aridoamerica, El Bajío saw relatively few permanent settlements and big civilizations during Pre-Columbian history, being mostly inhabited by the Otomi and semi-nomadic tribes known to the Aztecs as the "Chichimeca" peoples (poorly attested conglomerate of Uto-Nahua groups, from whom the Toltec and the Aztecs were probably descended). The tribes that inhabited the Bajío proved to be some of the hardest to conquer for the Spanish—peace was ultimately achieved via truce and negotiation—but due to its strategic location in the Silver Route, it also drew prominent attention from Europe, and some of the flagship Mexican colonial cities were built there, such as Zacatecas and Guanajuato. Abundant mineral wealth and favorable farming conditions would soon turn the region into the wealthiest of New Spain. At the beginning of the 19th century, El Bajío was also the place of the ignition of the Mexican War of Independence, and saw most of its battles during the initial phase of the war, including the Cry of Dolores, the storming of the Alhóndiga de Granaditas and the Battle of Calderón Bridge.

Nowadays, the region features one of the strongest economies in Mexico and Latin America, drawing both domestic investment from the adjacent, industry-heavy State of Mexico, as well as foreign companies seeking cheap specialized labor and decent infrastructure (mostly American, Japanese and to some extent, European vehicle and electronics companies). The largest cities of the Bajío are Guadalajara, León, Santiago de Querétaro, and Aguascalientes.

The Bajío rose to world prominence during the three centuries of colonial rule, providing much of the mineral and agricultural wealth of the Spanish Empire. As such, it was also the birthplace of the Mexican War of Independence, during which criollo elites long established in the Bajío gathered the masses to revolt against Napoleonic rule in Spain, seen as a threat to the established order in America.

Recent archeological studies have discovered an extensive historic cultural tradition that is unique to the region, particularly along the flood plains of the Lerma and the Laja Rivers. The Bajío Culture flourished from 300 to 650 CE, with cultural centers ranging from El Cóporo in the far north of Guanajuato to Plazuelas in the far southwest. More than 1,400 sites have been discovered throughout the state of Guanajuato, with only the sites of Cañada de la Virgen, El Cóporo, Peralta, and Plazuelas having received extensive study.

The Bajio from pre-Columbian times is best remembered from the Chichimeca nations, the name given by the Mexicas to a group of indigenous chiefdoms without clear states, boundaries or dwelling places, who inhabited the center and north of the country, such as Guachichiles, Guamares, Pames, Tecuexes, among others.

By 1536 the Spanish and the Otomí leader Conín had founded the multi-ethnic city of Santiago de Querétaro. On the dawn of European expansion with the expedition of Nuño de Guzmán and the Spanish acquisition of the Purepecha Empire after 1530, the region north of the limits of Mesoamerican civilization was also known as the Great Chichimeca, and was the epicenter of the Chichimeca War in the 16th century. The Chichimeca War confronted the Holy Roman Empire and Habsburg Europe at large under Charles V against the native chiefdoms of the Caxcans, the Zacatecs, the Guamares and other nomadic Uto-Nahuan peoples, with the goal of conquering their lands and exploiting silver discovered between 1540 and 1590. The resulting economic activity would quickly become the economic engine of the Kingdom of New Galicia, and the Viceroyalty of New Spain at large, serving as a pivotal hub for world commerce between Europe and Asia (see Global silver trade from the 16th to 19th centuries).

Valladolid (today Morelia), Guadalajara, among other cities were often founded with the goal to contain the "barbarian" tribes and protect Spanish families. The discovery of the mines of Zacatecas and Guanajuato, on the other hand, caused a high arrival of Spanish and Tlaxcaltec people to the area, which led to the founding of towns such as San Miguel el Grande (1542), Celaya (1571), Zamora (1574) Aguascalientes (1575) and León (1576), Durango, Chihuahua, Santa Fe Nuevo México: the so-called Silver Route of the Spanish treasure fleet. Meanwhile, king Philip II of Spain orchestrated most of the Counter-Reformation in Europe and the Fourth Ottoman–Venetian War in large part with the wealth provided by settlers, indigenous people and African slaves from the American colonial enterprise centered at the Bajío and Potosí, Bolivia. For much of the 16th century, the Bajío was characterized by its coming and going of cattle from Querétaro and Lake Chapala, by the ongoing silver rush and by the "warlike spirit" arising from the Chichimeca War,which culminated with severe reductions in Chichimeca populations due to war and smallpox. The Chichimecas were reduced to a few settlements in the highlands or immersed in the new order.