An impressionist is a performer whose act consists of giving the "impression" of being someone else by imitating the other person's voice and mannerisms.

The word usually refers to a professional comedian who specializes in such performances, has developed a wide repertoire of impressions, and regularly seeks to add to them, often to keep pace with current events. Someone who imitates one particular person without claiming a wide range, such as a lookalike, is instead called an impersonator. In very broad contexts, "impersonator" may be substituted for "impressionist" where the distinction between the two is less important than avoiding confusion with the use of "impressionist" in painting and music.

Usually, the most "impressive" aspect of the performance is the vocal fidelity to the target — usually a politician or famous entertainer. Props may also be employed, such as glasses or hats, but these are now considered somewhat old-fashioned and cumbersome: the voice is expected to carry the act.

Because animated cartoons often lampoon famous people (sometimes obliquely), a facility for impressions is one of the marks of a successful voice actor. Many cartoon characters are intended to be recognized by the audience as evoking a specific celebrity, even when not explicitly named. With such indirect references, the entertainment value does not lie so much in the technical achievement of exactly reproducing the voice so much as in merely making it recognizable; the joke lies in the reference to a celebrity, not in its rendition.

Impressionist performances are a classic Casino entertainment genre.

In any case, there is a difference between being able to do "impressions" and being an "impressionist," which usually refers to a stage performer.