In promotion and of advertising, a testimonial or show consists of a person's written or spoken statement extolling the virtue of a product. The term "testimonial" most commonly applies to the sales-pitches attributed to ordinary citizens, whereas the word "endorsement" usually applies to pitches by celebrities. Testimonials can be part of communal marketing.

Advertisers have attempted to quantify and qualify the use of celebrities in their marketing campaigns by evaluating their awareness, appeal, and relevance to a brand's image and the celebrity's influence on consumer buying behavior.