A quinceañera (also fiesta de quinceañera, quince años, fiesta de quince años, quinceañero and quinces) is a celebration of a girl's 15th birthday. It has cultural roots in Mexico and Spain and is widely celebrated by girls throughout Latin America. The girl celebrating her 15th birthday is a quinceañera (Spanish pronunciation: [kinseaˈɲeɾa]; feminine form of "15-year-old"). In Spanish, and in Hispanic America, the term quinceañera is reserved solely for the honoree; in English, primarily in the United States, the term is used to refer to the celebrations and honors surrounding the occasion.

This birthday is celebrated differently from any other as it marks the transition from childhood to young womanhood. Historically, in the years prior to their 15th birthdays, girls learned about cooking, weaving, and childbearing from the elder women in their communities in preparation for their future roles as wives. During the celebration the girl's father would present her to potential suitors.

In the past, parallel customs could be found in Southern Europe, mainly Spain and France. Today, the custom remains strongest in Mexico, its likely country of introduction during the viceregal or Mexican imperial periods. However, it is widely celebrated in Spanish-speaking countries in the Americas. The grandest parties are comparable to British and US debutante balls. The celebrations themselves vary significantly in different countries; for example, the festivities in some have taken on more religious overtones than in others. Nowadays, the quinceañera is also celebrated by many Latino Americans in the United States, each according to their traditions.

In Brazil, a Portuguese-speaking country, a similar celebration is called festa de debutantes, baile de debutantes or festa de quinze anos. In the French Caribbean and French Guiana, it is called fête des quinze ans.