Quarteto em Cy (a play on words of the Portuguese for Quartet in B by poet and lyricist Vinicius de Moraes) was a Brazilian girl group originally composed of four sisters hailing from Ibirataia, a town located in the Brazilian state of Bahia: Cybele, Cylene, Cynara and Cyva – their real first names.

Cyva, the leader of the group, then moved to Rio de Janeiro, and persuaded her three sisters to join her there.

They then started to make regular appearances in the boates (small nightclubs) of Rio, particularly Bottle's bar and the legendary Zum-Zum, where they caught the attention of Vinicius de Moraes and other prominent figures of the bossa nova scene.

Connoisseurs of MPB and tropicalia have a particular regard for the first few years of their recording career, when they were signed to Brazil's most daring label, Elenco.

However, the formation with Cyva and Sonya was kept active for many years since 1980, by far the most stable period in the group's history.