Whole books have been written about the two important Spanish verbs: ser and estar. But don't worry, you won't have to read them. You will soon have a better understanding of how these two verbs are used, just by applying the following easy roles. 

Ser and estar can both be translated into English as "to be."
 

 

María es profesora. Juan es puertorriqueño. Yo estoy enfermo.

María is a teacher. Juan is Puertorican. I am sick.

So, when do you use ser and when estar? Here are some of the basic roles:

First, look for the word that stands after "to be". It can be a noun (table, teacher), a pronoun (this, he, her), an adjective (green, sick, ripe), a past participle (closed, opened), a present participle, also called gerund (doing, dancing)or a preposition (in, from).

 Noun

Ser is used to link two nouns or a noun and a pronoun. Both nouns or pronouns may appear in the sentence o merely be understood. Therefore, if "to be" is followed by a noun (what? , who?), use always ser: 
 

 

María is a teacher.  María is a good teacher.  It is one o' clock.

María es profesora.  María es una buena profesora.  Es la una.

Notice that there is no equivalent for the English article ("a")  The noun can be modified by an adjective. In this case there is an article in Spanish as well.  The article "la" before indicates that "una" is used as a noun.

Pronoun

 Ser is used to link two pronouns or a noun and a pronoun. Both nouns or pronouns may appear in the sentence o merely be understood. Therefore, if "to be" is followed by a pronoun, use always ser: 

 

Who is it? It's me.  What time is it?

¿Quién es? Soy yo  ¿Qué hora es?

There is no equivalent for "it" in Spanish, in this case.  Notice that there is no equivalent for the English "it"

Adjective

 If it is an adjective, you can use either ser or estar, depending on what the meaning of the adjective in the sentence is or which meaning you would like the adjective to have in this specific sentence. Most adjectives can be used with both verbs, but resulting in different meanings.

 Use ser before adjectives to refer to the objective and inherent quality or the normal, generic and permanent condition of something or someone, such as nationality, age, physical, intelectual and moral atributes, personality, religion, color, etc.: 
 

 

My friends are Spanish.  Many Hispanics are catholic.  Our house is white.

Mis amigos son españoles?  Muchos hispanos son católicos?  Nuestra casa es blanca?

(Nationality). Notice the lower case in Spanish.  (Religion). Notice the agreement beween "hispanos" and "católicos".  (Color). Notice the agreement beween "casa" and "blanca".

Use estar before adjectives to indicate that the condition expressed by the adjective results from a change (a kind of adjectives are past participles like built, bought, made, seen, opened, etc.), and to refer to the subjective impression of the speaker. Estar is therefore used to describe subjective feelings about the quality of something or someone, and for changing conditions like someone's health, feelings, temporary states of the mind, etc. Often sensual perception is emphasized in the usage, ie the subject may be shown to taste, look, feel or seem to be a certain way on a certain occasion: 
 

 

Ricardo is sick today.  I have the impression that the water is very cold today.  You are (look) very handsome today.

Ricardo está enfermo hoy  Me parece que está muy fría el agua hoy?  Estás muy guapo hoy?

Temporary and changing condition.  Subjective feeling. Notice the agreement beween "agua" and "fría".  Subjective impression, judgement.

Now that you know the two basic roles determining wether to use ser or estar to translate the English "to be" + adjective, you will be able to understand the differences between 
 

 

1. El agua es fría. (The water is cold.) 2. La manzana es verde. (The apple is green.) 3. El profesor es aburrido. (The teacher is boring.)

and and and

1a. El agua está fría. 2a. La manzana está verde.  3a. Hoy el profesor está muy aburrido.

1. = Inherent quality of water when not heated.
1a. = Ye, the water feels very cold today. I am not going to go in today.

 2. = We are talking about the naturalcolor of this variety of apple, for example "Granny".
2a. = Changing characteristic. The apple is not ripe yet.

 3. = Normal, inherentcharacteristic of this teacher. He is a boring teacher.
3a. = Temporary characteristic. What he does with us today is boring.

 The choice of ser or estar in this kind of sentences is crucial to the meaning. A change of the verb will change the meaning of the sentence. Sometimes the differences are very subtle and fine, and sometimes very big. Here are some more examples: 
 

 

Lola es delgada Lola está delgada.	Lola is thin (She is a thin person.) Lola is thin. (She has gotten thin.)
Mario es nervioso. Mario está nervioso.	Mario is nervous. (He is a nervous person.) Mario is feeling nervous. (Mario has gotten nervous/ seems nervous to me.)
Fernando es listo. Fernando está listo.	Fernando is clever. Fernando is ready.
Los hombres son vivos. Los hombres están vivos.	The men are sharp/ quick. The men are alive.
La carne es rica (mala). La carne está rica (mala).	Meat is delicious (awful). (in general) This meat is/ tastes delicious (awful). (specific dish)
Juan es pesado. Juan está pesado.	Juan is an annoying, tiresome and boring person. (his character) Juan is heavy. (he is over weight)

Past Participle

 Before past participles (closed, opened, done, sold) you may use either ser or estar depending on what you want to say.

 Use ser to say that "something is/ was/ has been/ will be/ should be etc. done by someone. This is called passive voice. A passive sentence describes a process, the same way an active sentence does. The only difference is in that the speaker thinks that who does it, the subject, is not important, secundary or not known. A passive sentence can usually transformed into an active (regular) sentence: 

The house was built by his father. (= passive voice)
His father built the house. (= active voice)

 

The house was built by his father	La casa fue construida por su padre
The financial crisis will never be solved.	La crisis financiera nunca será resuelta.	Notice that the actor, who acually "resolves the crisis" is omited.

Use estar to translate "to be" + past participle to express the result of a process: 

 

Now the house is built.	Ahora La casa está construida.	The result of "the father building the house" or "the house beeing built by the father"
The financial crisis is eventually solved.	La crisis financiera finalmente está resuelta.	The result of whoever "solving the crisis" or "the crisis beeing solved by whoever".

Notice the similarities of past participles with the adjectives described in the paragraphe about estar + adjective. Present Participle/ Gerund.
Present participles or gerunds are the "-ing" form of verbs in English (playing, dancing, singing, etc.). To translate them, use always estar: 
 

 

The children are playing soccer	Los niños están jugando al fútbol.	"To play a game" in Spanish is always "jugar a".
The students are studying.	Los estudiantes están estudiando para un examen.

Preposition

 Preposition that may follow "to be" are from, for, in/ on, and about to.

from:

 Use always ser:
 

 

Carlos is from Bogota	Carlos es de Bogotá.	Country of origin.
Rigoberta Menchú is from a poor family.	Rigoberta Menchú es de una familia pobre.	Socio economic origin.
My sueter is from wool	Mi suéter es de lana.	Material, what it is made from.
Who is this money from? (meaning: Who's money is this?)	¿De quién es este dinero?	Origin or possession. In English you often use expressions like "Who's money is this?" "It's my brother's money."

for:

 "To be for" is used to express destination, purpose and deadline, use always ser
: 

 

These flowers are for my mother	Estas flores son para mi mamá.
This pencil is to take notes.	Este lápiz es para tomar apuntes.
The homework is for tomorrow.	La tarea es para mañana.

in/ on:

 To translate "to be in" you can either use ser or estar.
If you would like to say that a thing or a person is located or present in a certain place (room, city, contry, region, etc.) use always estar: 
 

 

Cancún is in Mexico	Cancún está en México
The books are on the table.	Los libros están en la mesa.
The town hall is on the left side.	El ayuntamiento está a la izquierda.

Other expression in Spanish to describe the location of people or things are:
 
 

estar cerca de (to be close to), estar al lado de (to be next to), estar lejos de (to be far from), estar frente aor estar en frente de (to be in front of)

 

The party is in his house.	La fiesta es en su casa.
The big earthquake was in Central America.	El gran terremoto fue en América Central.

 Impersonal expression in English are: it is (im)possible, it is true, it is important, it is necessary, etc. To translate them use ser: 

es bueno/malo (it is good/ bad), es (im)posible (it is (im)possible), es verdad (it is true), es importante (it is important), es necesario (it is necessary)

 There are also many idiomatic expressions using estar, for which it would be very difficult to establish easy roles. You will have to memorize them or check them in a dictionary.
 
 

estar de buen/ mal humor (to be in a good/ bad mood), estar de acuerdo con (to be in agreement with), estar de regreso/ vuelta (to be back), estar de vacaciones (to be on vacation), estar de viaje (to be on a trip), estar de cabeza (), estar de rodillas (to be kneeling), estar de pie (to be standing), estar de espaldas (), estar en camino (to be on the way), estar de vendedor/ agente de viajes/ mesero/ ... (=estar trabajando de sales clerk/ travel agent/ waiter/ ...), estar para + infinitivo (to be about to + infinitive)