• The definite articles in Spanish are el, la, los, las

• El combines with a and de to form al and del:

I am going to the movies. I am leaving the movies.

Voy al cine. Salgo del cine.

You don't have to contract a or de with el if the article is part of a proper name, for example El Escorial: Yo voy a El Escorial.

• Articles agree in gender and number with the nouns they acompany: el padre, la madre, los niños, las muchachas.

There is only one exception: The masculine article el (and un) is used before feminine nouns that begin with a- or ha- when the first syllable of the noun carries the stress: el agua fría (the cold water), el alma perdida (the lost soul), el águila majestuosa (the majestic eagle), el hacha vieja (the old ax). If an adjective separates el and the noun, however, the "normal article" la is used: labuena alma. The plural forms are regular: las aguas frías (the cold waters), las almas perdidas (the lost souls), las águilas majestuosas (the majestic eagles), las hachas viejas (the old axes).
The names of the letters a: la a and hache: la hache, as well as the city The Hague: La Haya are not among the exceptions.

Question: The word academia (academy) is feminine. Do we say el academiaor la academia? (click here for the answer)
 

Uses:
 

• As a general rule we can say that the definite article is used more frequently in Spanish than in English. The subject of a sentence has always an article. The following are some situations where English does not use the definite article but Spanish does:

• with abstract nouns:

Terrorism has killed many innocent people.

El terrorismo a matado mucha gente inocente.

• with concrete nouns used in a general or generic sense (as representative of a class or group of things):

Vegetables are good for your health.

Las legumbres son buenas para la salud.

• with body parts and clothing items when it is obvious who the possessor is (instead of a possessive, for example my, your, his, our, in English:

My head hurts. He puts on his coat..

Me duele la cabeza. El se pone el abrigo..

• with tener + body parts where in English there is no article at all:

She has green eyes and blue hair.

Ella tiene los ojos verdes y el pelo azul.

• with days of the week where you use on in English:

On Sundays I like rest. On Monday I have to go back to work.

Los domingos me gusta descansar. El lunes tengo que volver al trabajo.

• to tell time

It is three o' clock.

Son las tres.

• with nouns in a series the article is repeated:

The north, south, east and west are the four main directions.

El norte, el sur, el este y el oeste son las cuatro direcciones principales.

• with titles such as doctor, señor, señora, señorita, profesor, etc. when referring to or talking about a person:

Miss Ramirez is sick. Professor Sánchez is back.

La señorita Ramírez está enferma. El profesor Sánchez está de vuelta.

The article is NOT used, however when you talk to the person directly: "¿Cómo está Ud., señor Pérez?"

• with surnames,  the masculine article los is used (and the family name in singular, of course): 

Millers have a new car.

Los Miller tienen un coche nuevo.

• with the names of languages and study subjects, except after the preposition en and the verbs hablar (to speak), escribir (to write), estudiar (to study), leer (to read), hablar (to speak), enseñar (to teach) and aprender (to learn):

Spanish is spoken by more than 400 million people.

El español lo hablan más de 400 millones de personas.

But: I speak/ teach/ learn Spanish.

Hablo/ enseño/ aprendo español.

• with nouns of weight and measure:

Bananas cost 300 Pesetas a pound. My boss pays me 10 Dolars an hour.

Los plátanos cuestan 300 pesetas la libra. Mi jefe me paga 10 dólares la hora.

• with nouns that follow gustar or similar verbs (like encantar, faltar, molestar, etc.) because they represent the subject:

I like tennis.

Me gusta el tenis.

• in certain semi idiomatic adverbial phrases where in English there is no article:

I almost never go to church. They took him to jail.

Casi nunca voy a la iglesia. Lo llevaron a la cárcel.

• with the names of certain countries or cities: (Originally the names of countries were alll used with the article, but there is a tendency in modern Spanish to follow the example of English and to use countries without articles. Some examples where Spanish still uses the article are el Brasil, el Canadá, el Ecuador, el Japón, el Perú.):

Last year we went to Peru.

El año pasado fuimos al Perú.

• In contrast to English, the article is not used with the numerical designation of rulers and dignitaries: 

Alfons the Thirteen. Elizabeth the Second. Charles the Fifth.

Alfonso Trece. Isabel Segunda. Carlos Quinto.

 

Answer: la academia because the rule is that we use el only when the first syllable carries the stress, which is not the case in academia.