In the active voice, the subject does the action. In the passive voice, the subject receives it. French builds the passive the same way English does, with être + a past participle, but the participle has to agree.
1. Formation: être + past participle (+ par + agent)
| Le chat mange la souris. | The cat eats the mouse. (active) |
| La souris est mangée par le chat. | The mouse is eaten by the cat. (passive) |
2. The participle agrees with the subject
Because the auxiliary is être, the past participle behaves like an adjective, it agrees in gender and number with the new subject.
| La souris est mangée. | (fem. sing., -e added) |
| Les souris sont mangées. | (fem. pl., -es added) |
3. Any tense works
| Ce livre est lu par des milliers de gens. | This book is read by thousands of people. (présent) |
| Ce livre a été écrit par Victor Hugo. | This book was written by Victor Hugo. (passé composé) |
| Ce livre sera publié l'an prochain. | This book will be published next year. (futur) |
4. Watch out: par vs. de for the agent
Usually par, but: verbs describing a lasting state, feeling, or description (entouré de, couvert de, aimé de, connu de, accompagné de) use de instead of par. La maison est entourée d'arbres. (The house is surrounded by trees.) Cet acteur est connu de tout le monde. (This actor is known by everyone.)
5. Often avoided: French prefers "on" + an active verb
Especially in speech, French tends to reach for on + an active verb rather than the passive, it's shorter and sounds more natural.
| On parle français ici. | French is spoken here. (more natural than "le français est parlé ici") |