Spanish nouns can be masculine (articles: el, un) and feminine (articles: la, una).

Nouns ending in -o and -r are mostly masculine, eg. hueso, cabello, color. Nouns na -a (not denoting men) are generally feminine (eg. casa, hija). Similarly, nouns ending in -d, -z, -ión, -is (verdad, unión, paz, tesis).

In the case of endings other than those listed, the gender of the noun is difficult to predict, although the masculine gender is somewhat more common. The gender of the noun is usually given in the dictionary.

Exceptional forms:
Despite the ending -a masculine are :
- the noun el día = day, and also el mapa
- a number of nouns in -ma (loaned from Greek): el sistema, el problema, el programa, el idioma, el tema, el aroma
- names of people na -a, especially na -ista, if they mean men: el turista, el pianista, el comunista, el atleta, el poeta (but these nouns become feminine when they denote women: la turista = female tourist).

Despite the ending -o, feminine are are:
- la mano = hand
- a certain number of abbreviated nouns: la foto (from a photographer), la moto (from a motocicleta), la radio.