Based in Navarre, Club Atlético Osasuna, commonly known as Osasuna, was founded in 1920. In 1932 the club reached the Segunda División, the second tier of the Spanish league system, for the first time and by the 1934-35 season, Osasuna were playing in the Primera División.
Although the club has historically moved between the first, second and third tiers, Osasuna have remained in the Primera División since 2000-01. In 2005, Osasuna reached the final of the Copa del Rey, where they met Real Betis. After falling behind, Osasuna equalised in the 82nd minute, forcing the game to extra time. Unfortunately, Betis went on to win the match in the second period of extra time, but it remains the closest the club has come to winning a major national trophy.
The club's best ever league performance is 4th place, which was achieved in both the 1990-91 and 2005-06 seasons. Although the latter gained them entry to the Champions League, they went out in the qualifying rounds. In total, Osasuna have qualified for the UEFA Cup on five occasions. Their most successful European venture was in 2006-07, when the club reached the semi finals of the competition, though they were eventually knocked out by fellow Spanish club Sevilla.
Noteable former Osasuna players include Carlos Cuéllar, Jaroslav Plašil, Pablo Orbaiz, Pierre Webó, Ludovic Delporte, Walter Pandiani and former club captain César Cruchaga, who spent the entire duration of his career with the club, making almost 450 appearances in total.
Since 1967, Osasuna's home ground has been the Estadio El Sadar, a multi-use stadum which was formerly called Reyno de Navarra for sponsorship reasons. During the stadium's early years, it could hold around 25,000 fans, although subsequent renovations and the implementation of all-seater stands has reduced its capacity to today's number, which stands at 19,553.