Athletic Club, commonly known as Athletic Bilbao

 The club has played in the Primera División of La Liga since its start in 1928. They have won La Liga on eight occasions. In the historical classification of La Liga Athletic Bilbao are in 4th place and one of only three clubs which have never been relegated from La Liga (the others being Real Madrid and Barcelona). The club also has a women's team, which has won four championships in the Spanish Superliga.

They are known as the Los Leones (the lions) because their stadium was built near a church called San Mamés (Saint Mammes). Mammes was an early Christian thrown to the lions by the Romans. The lions refused to eat Mammes and he was later made a saint. The San Mamés Stadium is hence nicknamed "the football cathedral".

The club is known for its cantera policy of bringing young Basque players through the ranks, as well as recruiting top Basque players from other clubs (like Joseba Etxeberria or Javi Martínez). Athletic official policy is signing professional players native to the greater Basque Country, including Biscay, Guipúzcoa, Álava and Navarre (in Spain); and Labourd, Soule and Lower Navarre (in France). Still, in recent times, this policy has been somewhat relaxed and players with direct Basque ancestry or with no Basque ancestry but formed in Basque clubs have played for the team. This has gained Athletic both admirers and critics. The club has been praised for promoting home grown players and club loyalty. Athletic is one of only four professional clubs in Spain (the others being Real Madrid, Barcelona and Osasuna) that is not a sports corporation; the club is owned and operated by its associates (socios).