“Por” means “for”, “because of”, “by” and several other meanings depending on the context.

Usage:

1. To express gratitude or apology

Example: ¡gracias por la ayuda! (Thanks for the help!)

2. For multiplication and division

Example: Dos por dos son cuatro. (Two times two equals four)

3. For velocity, frequency and proportion

Example: Voy al restaurante cinco veces por semana. (I go to the restaurant five times a week)

4. Meaning “through,” “along,” “by” or “in the area of”

Example: Andamos por el parque. (We walk through the park)

5. When talking about exchange, including sales

Example: Él me dio diez dólares por el libro. (He gave me ten dollars for the book)

6. To mean “on behalf of,” or “in favor of,”

Example: No voté por nadie. (I didn’t vote for anyone)

7. To express a length of time

Example: yo estudié por dos horas. (I studied for two hours)

8. To express an undetermined, or general time, meaning “during”

Example: se puede ver las estrellas por la noche. (Stars can be seen at night)

9. For means of communication or transportation

Example: prefiero viajar por tren y hablar por teléfono. (I prefer to travel by train and talk by phone)

10. In cases of mistaken identity, or meaning “to be seen as”

Example: me tienen por loco. (They think I’m crazy)

11. To show the reason for an errand

Example: voy por las frutas (in Spain, “voy a por las frutas”). (I go to get the fruits)

12. When followed by an infinitive, to express an action that remains to be completed, use “por + infinitive”

Example: la cena está por prepararse/cocinarse. (The dinner is yet to be prepared)

13. To express cause or reason

Example: el hombre murió por falta de agua. (The man died due to lack of water)

14. “Estar por” means to be in the mood, or inclined to do something

Example: estoy por tomar café. (I feel like having some coffee)

15. In passive constructions

Example: el libro fue escrito por Octavio Paz. (The book was written by Octavio Paz)

Some idiomatic expressions with “Por”: