Club Atlético Osasuna was founded on 24 October 1920 in Pamplona, the capital of Navarre, through the merger of two local clubs. The club's name comes from the Basque word for "health", carrying connotations of strength and vigour — making Osasuna the only La Liga side with a Basque-language name, a distinction that speaks to the region's deep cultural identity. Red and navy blue have been the club's colours throughout its existence, earning the team its enduring nickname "Los Rojillos" (The Little Reds).
Osasuna's path through Spanish football has been one of persistent determination rather than sustained dominance. After reaching La Liga for the first time in the mid-1930s, the club spent decades cycling between the top two divisions. Their proudest league finishes came in the 1990–91 and 2005–06 seasons, when they placed fourth in La Liga — the latter finish earned qualification for the UEFA Champions League qualifying rounds. Though Hamburg eliminated them before the group stage, Osasuna went on to enjoy a remarkable run in the 2006–07 UEFA Cup, defeating Rangers and Bayer Leverkusen before falling to eventual winners Sevilla in the semi-finals.
In cup competition, Osasuna reached the Copa del Rey final twice, in 2005 and 2023, losing on both occasions. The club operates on a member-ownership model, one of only four La Liga clubs to do so, and prides itself on developing talent through its cantera. Their fiercest rivalry is with Real Zaragoza from the neighbouring Aragon region, a fixture known for its intensity. In recent seasons Osasuna has established itself as a stable La Liga presence, including a seventh-place finish in 2022–23.