An impersonal verb is a verb that cannot take a true subject, because it does not represent an action, occurrence, or state-of-being of any specific person, place, or thing. Verbs indicating weather, such as "to rain," are often impersonal.

In some languages, such as English and French, an impersonal verb always takes the impersonal pronoun ("it" in English, "il" in French) as its subject: "it snowed yesterday"; "il a neigé hier."

In some other languages, such as Spanish, an impersonal verb takes no subject at all, but is conjugated as though it had a third-person, singular subject: "nevó ayer."

An impersonal verb is different from a defective verb in that with an impersonal verb, only one possible subject is meaningful, whereas with a defective verb, certain choices of subject might not grammatically possible, because the verb does not have a complete conjugation. For a more in-depth comparison, see defective verb.