Club Atlético Newell's Old Boys (Spanish pronunciation: [ˈkluβ aˈtletiko ˈɲuls olˈβojs]) is an Argentine sports club based in Rosario, Santa Fe. The club was founded on 3 November 1903, and is named after Isaac Newell of the English county of Kent, one of the pioneers of Argentine football.

A founding member of Liga Rosarina de Football, the club affiliated to the Argentine Football Association (AFA) in 1939. Since then, Newell's Old Boys have taken part in tournaments organised by the body. The club have won six Argentine Primera División championships plus three national cups throughout their history. Newell's have also been twice Copa Libertadores runner-up (in 1988 and 1992).

The club's football stadium is the Estadio Marcelo Bielsa, named after the team's former player and manager Marcelo Bielsa (twice champion, and runner-up of one Copa Libertadores). Newell's play the Rosario derby against Rosario Central, a club with whom they have a huge historical rivalry.

Newell's are also notable for their youth divisions, being one of the clubs with most national titles in AFA's youth tournaments. Players from the club's youth who have represented Argentina at World Cups are Gabriel Batistuta, Éver Banega, Walter Samuel, Américo Gallego, Jorge Valdano, Gabriel Heinze, Roberto Sensini, Mauricio Pochettino, Lionel Scaloni and Maxi Rodríguez, among others. Lionel Messi also played in the club's youth, but left at a young age to play for Barcelona to seek treatment for his growth hormone deficiency, while Diego Maradona played briefly for the first team in 1993.

Other sports practised at this club are basketball, boxing, field hockey, martial arts, roller skating, volleyball and American football.