Passive voice emphasizes the action's recipient rather than the doer. The basic structure moves the object of an active sentence to subject position and adds a form of "be" plus the past participle: "The cat chased the mouse" becomes "The mouse was chased by the cat." The agent (doer) introduced by "by" is optional and often omitted when unknown or unimportant. Different tenses require different forms of "be" combined with the past participle.
Tense-specific passive structures follow predictable patterns. Present simple passive uses "am/is/are + past participle" ("The cake is baked by my mother"). Past simple passive uses "was/were + past participle" ("The book was written by her"). Present continuous passive uses "be + being + past participle" ("A new bridge is being built"). Present perfect passive uses "have/has been + past participle" ("The work has been completed"). Future passive uses "will + be + past participle" ("The report will be written"). Passive infinitives take the form "to + be + past participle" ("She wants to be promoted"), and modals combine as "modal + be + past participle" ("The rules must be followed").