Francesco Stephen Castelluccio (born May 3, 1934), better known by his stage name Frankie Valli, is an American singer and occasional actor, best known as the lead vocalist of the Four Seasons. He is known for his unusually powerful falsetto voice.

Valli scored 29 top-40 hits with the Four Seasons, one top-40 hit under the Four Seasons alias the Wonder Who?, and nine top-40 hits as a solo artist. As a member of the Four Seasons, Valli's number-one hits include "Sherry" (1962), "Big Girls Don't Cry" (1962), "Walk Like a Man" (1963), "Rag Doll" (1964), and "December, 1963 (Oh, What a Night)" (1975). His recording of the song "Can't Take My Eyes Off You" reached number two in 1967. As a solo artist, Valli scored number-one hits with the songs "My Eyes Adored You" (1974) and "Grease" (1978).

Valli, Tommy DeVito, Nick Massi, and Bob Gaudio—the original members of the Four Seasons—were inducted into the Rock and Roll Hall of Fame in 1990 and the Vocal Group Hall of Fame in 1999. Valli is also a 2010 inductee of the New Jersey Hall of Fame, with the Four Seasons (Gaudio, Massi, DeVito, and Joe Long) inducted separately in 2017 and Valli speaking on Massi's behalf. Valli was awarded a star on the Hollywood Walk of Fame in May 2024, a joint star for both the Four Seasons and him. Valli appeared in person to accept the honor with his wife and two of his sons, and Gaudio sent a recorded acceptance speech. In February 2025, Valli was awarded a Grammy Lifetime Achievement Award, his first-ever Grammy.