vertically striped green-white-red national flag with a central coat of arms (arms, coat of) featuring an eagle, a cactus, and a serpent. The flag has a width-to-length ratio of 4 to 7.

The struggle for Mexican (Mexico) independence took place under a number of flags, but, when it was finally achieved in 1821 under the conservative Iguala Plan, a tricolour of green-white-red was officially established. This design may have been influenced by the French Tricolor (France, flag of), but the colours were distinctively Mexican. Green symbolizes independence, white is for the Roman Catholic religion, and red is for union—the “Three Guarantees” of Iguala. That political compromise allowed Mexico to free itself from Spain while preserving the supremacy of Roman Catholicism and of the social system in which the privileged Creoles ruled over those of mixed ethnic background and the Indian majority.

The central emblem on the tricolour shows in graphic form the foundation myth of the ancient Aztec empire. The scene depicted is the one that the Indian founders of Tenochtitlán (now Mexico City) supposedly saw in 1325, which met their prophecies of the predestined site for their capital—namely, an eagle with a snake in its beak standing on a cactus growing out of rocks in the middle of water. Various artistic renditions of this scene have been utilized over the years by different regimes to symbolize both Mexican nationality and adherence to changing political philosophies. For example, from 1821 to 1823 and from 1864 to 1867, Mexico was an empire and the eagle on the flag was crowned. The current version of the arms shows a wreath of oak and laurel tied with a ribbon in the national green-white-red colours. This version of the flag was made official on September 17, 1968.