Aqualung is the fourth studio album by the rock band Jethro Tull. Released in 1971, Aqualung, despite the band's disapproval, is regarded as a concept album featuring a central theme of “the distinction between religion and God”. The album's “dour musings on faith and religion” have marked it as “one of the most cerebral albums ever to reach millions of rock listeners”. Aqualung‍‍ '​‍s suc­cess marked a turning point in the band's career, who went on to become a major radio and touring act.

Review
“Released at a time when a lot of bands were embracing pop-Christianity (à la Jesus Christ Superstar), Aqualung was a bold statement for a rock group, a pro-God antichurch tract that probably got lots of teenagers wrestling with these ideas for the first time in their lives. This was the album that made Jethro Tull a fixture on FM radio, with riff-heavy songs like "My God,” “Hymn 43,” “Locomotive Breath,” “Cross-Eyed Mary,” “Wind Up,” and the title track. And from there, they became a major arena act, and a fixture at the top of the record charts for most of the 1970s. Mixing hard rock and folk melodies with Ian Anderson's dour musings on faith and religion (mostly how organized religion had restricted man's relationship with God), the record was extremely profound for a number seven chart hit, one of the most cerebral albums ever to reach millions of rock listeners. Indeed, from this point on, Anderson and company were compelled to stretch the lyrical envelope right to the breaking point. [In the digital age, Aqualung has gone through numerous editions, mostly owing to problems finding an original master tape when the CD boom began. When the album was issued by Chrysalis through Columbia Records in the mid-'80s, the source tape was an LP production master, and the first release was criticized for thin, tinny sound; Columbia remastered it sometime around 1987 or 1988, in a version with better sound. Chrysalis later switched distribution to Capitol-EMI, and they released a decent sounding CD, as well as a 25th anniversary edition in 1996. Fifteen years later, the 40th anniversary was marked with varying editions, most of them including a previously unreleased stereo mix of the album plus additional recordings from 1970–71.]" B Eder – Allmusic.com