Classic 21 is a Belgian public radio station operated by RTBF (Radio-télévision belge de la Communauté française). Launched in 2004, it replaced Radio 21 and focuses on classic rock and pop music from the 1960s to the 1990s. Broadcasting from Mons, Classic 21 caters to a French-speaking audience across Wallonia and Brussels.

The station features popular programs like "Les Classiques du dimanche matin" hosted by Marc Ysaye, which showcases music from the 1960s-1980s, and Walter de Paduwa's long-running "Doctor Boogie" show, on air since 1994, featuring blues, boogie, and zydeco music.

Classic 21's programming includes a mix of classic rock hits, themed shows, and music history segments. It has maintained a strong presence in the Belgian Francophone radio market, reaching a 9% market share in 2016.

In addition to its main broadcast, Classic 21 offers several digital-only channels focusing on specific decades and genres, such as 60s, 70s, 80s, blues, and metal, expanding its reach to diverse rock and pop music enthusiasts.