An "it girl" is an attractive young woman, who is perceived to have both sex appeal and a personality that is especially engaging.

The expression it girl originated in British upper-class society around the turn of the 20th century. It gained further attention in 1927 with the popularity of the Paramount Studios film It, starring Clara Bow. In the earlier usage, a woman was especially perceived as an "it girl" if she had achieved a high level of popularity without flaunting her sexuality. Today, the term is used more to apply simply to fame and beauty. The Oxford English Dictionary distinguishes between the chiefly American usage of "a glamorous, vivacious, or sexually attractive actress, model, etc.", and the chiefly British usage of "a young, rich woman who has achieved celebrity because of her socialite lifestyle". The terms "it boy" or "it man" are sometimes used to describe a male exhibiting similar traits.