The National Symphony Orchestra (Spanish: Orquesta Sinfónica Nacional, OSN) is the most important symphony orchestra in Mexico. With its origins traced back as 1881, along with the Boston Symphony Orchestra, it is the second-oldest symphony orchestra in the American continent. The orchestra does not have a permanent venue but performs regularly in the Grand Hall of the Palace of Fine Arts (Palacio de Bellas Artes) in Mexico City.

Not to be confused with the Orquesta Sinfónica del Estado de México (OSEM) or Symphony Orchestra of the State of Mexico, founded in 1971, the National Symphony Orchestra of Mexico, as a branch of the Instituto Nacional de Bellas Artes, was created by presidential decree of Miguel Alemán on 18 July 1947, under the name of National Conservatory Symphony Orchestra. Before that, however, there was a predecessor orchestra known as the Symphony Orchestra of Mexico (September 2, 1928 – March 8, 1949), a nonprofit organization founded and conducted by Mexican composer, conductor, teacher, journalist and visionary arts leader Carlos Chávez. On 1 August 1947, Chávez appointed Blas Galindo as the new director of the National Conservatory, official seat of the new orchestra. Chávez reports that the National Symphony Orchestra gave its first official performance on 30 October 1947 at the Palace of Fine Arts, under the baton of Eduardo Hernández Moncada, its first music and artistic director.

Another decree on April 25, 1949, changed the name of the ensemble to National Symphony Orchestra (Orquesta Sinfónica Nacional or OSN); first, to emphasize its professional character—it had the best musicians in the country—and to avoid confusing it with a student ensemble, despite Chávez's having from the very beginning considered the orchestra a national symphony, linked in some aspects to the most important music education institution, the National Conservatory; and second, Chávez wanted to highlight that “a National Symphony, by definition, is a State institution,” and the government had recognized the need to support an institution of public interest.