Both verbs, ser and estar, are equivalent to the English verb to be; however, they have very specific meanings and are NOT interchangeable. NOTE in the following examples how the meaning of a sentence changes: e1x16xx
La Miss Universo es linda./Miss Universe is pretty.
La Miss Universo esta linda./ Miss Universe looks pretty (at this specific moment).

El niño es listo./ The child is smart.
El niño esta listo./ The child is ready.

Mi madre es aburrida./ My mother is boring (she is a boring person).
Mi madre esta aburrida./ My mother is bored.

Mi hijito es vivo./ My little son is smart.
Mi hijito esta vivo./ My little son is alive.

SER / TO BE
Pronoun Present Past Future Conditional yo/ I soy fui seré seria tú/ you eres fuiste seras serias
él, ella, Ud./ he, she, you es fue sera seria nos./ we somos fuimos seremos seriamos vos./you sois fuisteis seréis seriais ellos, Uds./ they, you son fueron seran serian

1. Ser/ to be is used to describe essential or inherent characteristics or qualities:
Basic aspects: color, shape, material of which something is made out of, size, physical characteristics, and personality.
La nieve es blanca./ The snow is white.
La tierra es redonda./ The earth is round.
El saco es de lana./ The jacket is wool.
Yo soy alta./ I am tall.
Mi socio es extrovertido./ My partner is outgoing.
2. Possession.
El auto es mio./ The car is mine.
3. Relationship.
Ella es mi prima./ She is my cousin.
4. Profession.
Son cirujanos plasticos./ They are plastic surgeons.
5. Nationality.
Soy argentina./ I am Argentine.
6. Origin.
El interventor es de La Paz./ The auditor is from La Paz.
7. Ser/ to be is used to indicate marital status.
Ella es divorciada./ She is divorced.
8. Expressions of time and dates.
Es la una./ It's one o'clock.
Hoy es jueves./ Today is Thursday.
9. Events taking place.
La fiesta es esta noche./ The party is tonight.
10. Passive voice.
La casa fue incendiada./ The house (was) burned down.
11. Impersonal expressions.
Es imposible hablar con ellos./ It's impossible talking to them.
12. Noun and adjective complement (A complement completes the sentence by describing or defining the subject).
Mi suegra es una abuela maravillosa./ My mother-in-law is a wonderful grandma.
Ella es Ana./ She is Ana.
El compasivo es él./ The compassionate one is he. (Remember that the verb to be is transitory; therefore, he is used instead of him.)
ESTAR / TO BE
Estar is used to express location, transitory aspects, and characteristics that are NOT inherant property of a noun, such as how something/someone looks, feels or tastes at a given moment.
Pronoun Present Past Future Conditional yo/ I estoy estuve estaré estaria tú/ you estas estuviste estaras estarias
él, ella, Ud./ he, she, you esta estuvo estara estaria nos./ we estamos estuvimos estaremos estariamos vos./you estais estuvisteis estaréis estariais ellos, Uds./ they, you estan estuvieron estaran estarian
1. Location or position of people and things.
El restaurante esta en la esquina./ The restaurant is at the corner.
Los inversores estaran en Venezuela./ The investors will be in Venezuela.
2. Transitory, unusual, recently changed or constantly changing state or condition.
Pablo estuvo enfermo./ Pablo was sick.
El café esta frio./ The coffee is cold.
3. Results of an action.
Nuestros problemas estaran resueltos pronto./ Our problems will be solved soon.
4. State or condition of a subject.
El rehén esta vivo./ The hostage is alive.
5. Progressive tenses.
El lunes estaremos celebrando nuestro triunfo./ On Monday we'll be celebrating our triumph.
6. Weather expressions.
Esta lloviendo./ It's raining.

IDIOMATIC EXPRESSIONS
Estar acostumbrado/ to be accustomed to
Estar conforme/ to be satisfied, in agreement
Estar de acuerdo/ to be in agreement
Estar de buen (mal) humor/ to be in a good (bad) mood
Estar apurado (a)/ to be in a hurry
Estar de vacaciones/ to be on vacation
Estar de vuelta/ to be back
Estar listo (a)/ to be ready
Estar de moda/ to be in fashion
Estar de viaje/ to be on a trip
Estar embarazada/ to be pregnant
Estar de rodillas/ to be kneeling