In linguistics, an impersonal verb is one that has no determinate subject. For example, in the sentence "It rains", rain is an impersonal verb and the pronoun it corresponds to an exophoric referent. In many languages the verb takes a third person singular inflection and often appears with an expletive subject. In the active voice, impersonal verbs can be used to express operation of nature, mental distress, and acts with no reference to the doer. Impersonal verbs are also called weather verbs because they frequently appear in the context of weather description. Also, indefinite pronouns may be called "impersonal", as they refer to an unknown person, like one or someone, and there is overlap between the use of the two.

Impersonal verbs appear only in non-finite forms or with third-person inflection. In the third person, the subject is either implied or a dummy referring to people in general. The term "impersonal" simply means that the verb does not change according to grammatical person. In terms of valency, impersonal verbs are often avalent, as they often lack semantic arguments. In the sentence It rains, the pronoun it is a dummy subject; it is merely a syntactic placeholder—it has no concrete referent. In many other languages, there would be no subject at all. In Spanish, for example, It is raining could be expressed as simply llueve.

Temperature expressions ("it is hot"), weather expressions ("it is snowing"), and daylight expressions ("it is dark") tend to lack independent participants with distinct semantic roles. While snow participates in snowing, very few other types of participants can participate, and the participant is indistinguishable from the event itself; this is similar to the phenomenon of cognate objects. In addition, the participating snow is non-specific, and lacks a clear semantic role. Therefore, assigning the participating snow the role of 'referent' in the default English expression "it is snowing" would seem inappropriate. Instead, linguistics classify the "is snowing" in "it is snowing" as an impersonal verb.

Meteorological expressions are often constructed with impersonal verbs in English. However, meteorological expressions are obviously not restricted solely to impersonal verbs, even in English; furthermore, different languages use different strategies for their default meteorological expressions and common idioms. In Palestinian Arabic, "Id-dunya ti-shti" translates to "It (the world) is raining" and uses a non-impersonal verb. "Vreme je sunčano", which means "the weather is sunny", is a common Serbian construction that uses a (non-impersonal) adverb rather than a verb.

When an agent is unspecified, impersonal verbs are also known as zero person construction, or impersonal construction. An implicit argument (an argument that is put forth without stating it directly) is present on a semantic level for both Estonian and Finnish. The Finnic impersonal construction enables an event or state to be described without specifying the identity of the agent (actor). Despite this, the interpretation of the impersonal includes a referent of some sort (dummy). The zero person is not entirely the same as an impersonal.

Finnish:

Sunnuntaina

Sunday-on