Matlatzinca is a name used to refer to different indigenous ethnic groups in the Toluca Valley in the state of México, located in the central highlands of Mexico. The term is applied to the ethnic group inhabiting the valley of Toluca and to their language, Matlatzinca. When used as an ethnonym, Matlatzinca refers to the people of Matlatzinco. Matlatzinco was the Aztec (Nahuatl) term for the Toluca Valley. The political capital of the valley was also referred to as “Matlatzinco;” this was a large city whose ruins are today known as the archaeological site of Calixtlahuaca. In Prehispanic times the Toluca Valley was the home to speakers of at least four languages: Otomi, Matlatzinca, Mazahua, and Nahuatl. Thus speakers of any of these languages could be called “Matlatzinca” if they resided in the Toluca Valley. When the Aztec native historical sources or the Spanish chroniclers refer to “the Matlatzinca” it is often not clear where they mean speakers of the Matlatzinca language, the peoples of the Toluca Valley, or even the inhabitants of Calixtlahuaca.