Glee is a musical comedy-drama television series that aired on Fox in the United States for six seasons from 2009 to 2015. It focuses on the high school glee club New Directions competing in the show choir competition circuit, while its members deal with relationships, sexuality and social issues.

The initial main cast encompassed club director and Spanish (later History) teacher Will Schuester (Matthew Morrison), cheerleading coach Sue Sylvester (Jane Lynch), guidance counselor Emma Pillsbury (Jayma Mays), Will's wife Terri (Jessalyn Gilsig), and eight club members played by Dianna Agron, Chris Colfer, Kevin McHale, Lea Michele, Cory Monteith, Amber Riley, Mark Salling and Jenna Ushkowitz. For the second season, formerly recurring cast members Mike O'Malley, Heather Morris and Naya Rivera were promoted to the main cast. In the third season the main cast remained at fifteen, with Harry Shum Jr. and Darren Criss promoted to it, while Gilsig and O'Malley no longer received star billing. The fourth season began with fourteen in the main cast, with Chord Overstreet being promoted, and Mays and Agron were removed and demoted to recurring cast. The fifth season saw the biggest change, with Monteith's death, and Morris, Riley, Salling and Shum all being switched to recurring status. At the same time, Jacob Artist, Melissa Benoist, Blake Jenner, Alex Newell and Becca Tobin were promoted to the main cast and are credited as such for the season, though they appear only in the first thirteen of the twenty episodes, after which New Directions is disbanded and the series shifts to the glee club alumni in New York City for the remainder of the season. The sixth and final season's main cast was reduced to nine: Colfer, Criss, Lynch, McHale, Michele, Morrison and Overstreet continued from the previous season, Riley returned to the main cast, and Dot-Marie Jones as football coach Shannon (later Sheldon) Beiste was promoted to it.

The series has many supporting characters, including faculty members, students and relatives of the glee club members. Broadway stars including Idina Menzel, John Lloyd Young, Jonathan Groff, Phoebe Strole and Kristin Chenoweth have been featured in guest roles. A number of the principal actors were cast directly from Broadway, while those without theatrical backgrounds were required to demonstrate singing and dancing as well as acting ability.