Please answer a question about the following article about FC Barcelona:

Barcelona is the only European club to have played continental football every season since 1955, and one of three clubs to have never been relegated from La Liga, along with Athletic Bilbao and Real Madrid. In 2009, Barcelona became the first club in Spain to win the treble consisting of La Liga, Copa del Rey, and the Champions League. That same year, it also became the first football club ever to win six out of six competitions in a single year, thus completing the sextuple, comprising the aforementioned treble and the Spanish Super Cup, UEFA Super Cup and FIFA Club World Cup. In the 2014–15 season, Barcelona won another historic treble, making them the first club in European football to win the treble twice.

What team has played continental football every season since 1955?
Barcelona