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. The term weather verb is also sometimes used, since such weather-indicating verb as to rain are usually impersonal.

In some languages, such as English, French and German, an impersonal verb always takes an impersonal "dummy pronoun" (it in English, il in French, es in German) as its syntactical subject:

It snowed yesterday.

Il a neigé hier. (French)

Es schneite gestern. (German)

In some other languages (necessarily null subject language and typically pro-drop languages), such as Portuguese, Spanish, Occitan, Catalan and Italian, an impersonal verb takes no subject at all, but it is conjugated in the third-person singular, which is much as though it had a third-person, singular subject:

Nevó ayer. (Spanish)

Nevou ontem. (Portuguese)

In some languages, some verbs meaning existence are also impersonal.

Há livros. / Há um livro. (Portuguese: There are books / There is a book)

Hay libros. / Hay un libro. (Spanish: There are books / There is a book)

In these languages, however, there may be personal verbs with more or less the same meaning:

Existem livros. / Existe um livro. (Portuguese: There exist books / There exists a book)

An impersonal verb is different from a defective verb in that with an impersonal verb, only one possible syntactical subject is meaningful (either expressed or not), whereas with a defective verb, certain choices of subject might not grammatically possible, because the verb does not have a complete conjugation.

Verb types