Aqualung was one of the first albums to be recorded at Island Studios out in London. While they were recording, Led Zeppelin was mixing their untitled fourth album in an adjoining studio. Aqualung was Jethro Tull's fourth studio album.
Side A begins with two sketches, including some characters that are less than reputable (Aqualung and Cross Eyed Mary). Then, it includes two autobiographical tracks, both written by Ian Anderson. They are about visiting his father when he was chronically ill.
- "Aqualung," the song, got its name from the gurgling sound of underwater diving gear which Anderson felt described the wheezing of the song's character. Anderson did not know that "Aqualung" was a trademark and not a generic phrase (the issue was settled quite amicably). 
Side B is about being "Pro-God, Anti-Church". This is because, as it states many times on side B, having an organized religion can restrict somebody to worshiping God in a certain way, thereby not enhancing it.
- The song "My God" first states that people have manipulated God for their purposes ("Locked him in his golden cage./Made him bend to your religion --"). Then, it goes on to state the atheist point of view ("He is the God of nothing --/If that's all that you can see."), and the Christian point of view ("You are the God of everything --/He's inside you and me."). It then says that people should lean on God gently, "And don't call on him to save you/From your social graces/And the sins you used to waive." Graces, in this sense, refers to charities, and most likely means that because throughout history, the church has generally helped the rich, the church is only doing the charities to make them look good. The sins that were waived refer to during the Protestant Reformation, when people would pay the church indulgences to have their sins forgiven. It then says that the church is wrapped in the chains of history, meaning that it cannot be forgotten just because it was the church doing it, showing it's also "earthly presence".
This was one of two Jethro Tull albums released using quadraphonic sound (the other is War Child). One difference between the actual album and between the quadraphonic version was that the song "Wind Up" was preformed in a higher key (this version is included in the re-release). Also, the song "Aqualung" has two riffs at the beginning of it instead of just one in the quadraphonic version.