Passive sentences emphasize the receiver of the action, by making what is normally the object of the verb the subject. Passive sentences are usually formed with the verb être and the past participle. The past participle will always agree with the subject. The perpetrator of the action need not be mentioned at all; if it is mentioned it is introduced by the preposition par and appears after the verb.
Malheureusement, Pierre a été mangé par des crocodiles.
In French, the passive is often avoided by using on, the "stand for just about anything" subject pronoun.
In addition, passive sentences are often formed with the pronominal. (See no external objects). Sometimes a pronominal has both passive and active interpretations:
While othertimes it is clearly passive: