What is the difference between por and para in Spanish?

Por and para are both words often used in place of the English word "for". However, por is generally used to convey more abstract concepts. This difference is difficult to grasp and even native speakers are known to occasionally confuse the two. For some basic guidelines, you can remember:

Para is used when you are speaking about:

Destinations (toward, in the direction of)

Salgo para los Estados pronto. I leave for the States soon.

Deadlines (by, for)

Tu retrato debe estar terminado para domingo. Your portrait should be done by Sunday.

Goals (in order to)

Para estar listo, preparar tus maletas la noche antes de tu viaje. In order to be ready, prepare your bags the night before your trip.

Purpose (for, used for)

Compré comida para la semana. I bought food for the week.

Recipient (for)

Cociné el desayuno para mi madre. I cooked breakfast for my mother.

Comparison with others or opinion (for, considering)

Para ser tan joven, Roberto es muy inteligente. For being so young, Roberto is very intelligent.

Para mi, el chocolate no es delicioso. For me, chocolate is not delicious.

Employment (for)

Trabajo para Boeing. I work for Boeing.

Use por when speaking about:

Motion or general location (along, through, around, by)

El hombre entró por la puerta. The man entered through the door.

Duration of an action (for, during, in)

Estudiará en Barcelona por un año. I will study in Barcelona for a year.

Reason or motive for an action (because of, on account of)

Son refugiados por razones políticas. They are refugees for political reasons.

Object of a search (for, in search of)

Fui a mi coche por mis libros. I went to my car for my books.

Means by which (by, by way of, by means of)

Hablamos por teléfono. We spoke by phone.

Exchange or subsitution (for, in exchange for)

Cambié mi sofá por un otro. I switched my couch for another.

Unit of measure (per, by)

Este coche puede ir 200 millas por hora. This car can go 200 miles per hour.

Agent in the passive voice (by)

Los regalos fue comprados por Laura. The gifts were bought by Laura.