Active voice is a grammatical voice common in many of the world's languages. It is the unmarked voice for clauses featuring a transitive verb in nominative–accusative languages, including English and most other Indo-European languages. A verb in such languages is usually in the active voice when the subject of the verb performs the action named.

Active voice is used in a clause whose subject expresses the main verb's agent. That is, the subject does the verb's designated action. A clause whose agent is marked as grammatical subject is called an active clause. In contrast, a clause in which the subject has the role of patient or theme is named a passive clause, and its verb is expressed in passive voice. Many languages have both an active and a passive voice and this allows for greater flexibility in sentence construction, as either the semantic agent or patient may take the subject syntactic role.

In a clause including an impersonal verb, the verb is active in form, but no agent is specified.