The Eagles' 'Their Greatest Hits (1971-1975)' is a remarkable album that has achieved unprecedented success, despite not being on any 'best album of all time' lists. Released 50 years ago, it has sold over 40 million copies, making it the most popular album in the US and one of the top five globally. This compilation album, which includes the band's signature song 'Hotel California' and other popular tracks, has resonated with audiences and become a cultural phenomenon. The album's success can be attributed to its ability to capture the essence of the Eagles' back catalogue and its alignment with the cultural moment of the mid-1970s. The Eagles reminded older listeners of the '60s, with a more polished and commercial sound, while also appealing to new fans with a chance to explore their music. The album's success is also a testament to the power of greatest hits albums, which have been a staple of the music industry for decades. However, the album's success has sparked debates about the value of greatest hits albums and their place in the music industry. Some argue that they are the preserve of fair-weather fans and lack the artistic integrity of full-length albums. Despite these criticisms, 'Their Greatest Hits (1971-1975)' remains a beloved and enduring album that has left a lasting impact on the music industry.