In the Aeroplane Over the Sea is the second and final studio album by the American band Neutral Milk Hotel, released on February 10, 1998, by Merge Records. The album is predominantly indie rock and psychedelic folk and is characterized by an intentionally low-quality sound. Traditional indie rock instruments like the guitar and drums are paired with less conventional instruments like the singing saw and uilleann pipes. The lyrics are surrealistic and opaque, exploring themes that range from nostalgia to love. An important influence for the album was The Diary of a Young Girl, a book of writings from the diary of Anne Frank.

In the Aeroplane Over the Sea was recorded at Pet Sounds Studio from July to September 1997. Producer Robert Schneider worked with bandleader Jeff Mangum to improve upon the low-quality sound of Neutral Milk Hotel's debut album, On Avery Island. Instead of using standard studio equipment like guitar pedals or effects units to induce distortion, Schneider developed a recording technique that involved heavy Dynamic range compression|compression. To promote the album, Neutral Milk Hotel undertook a tour of North America and Europe, and developed a reputation for chaotic and physically demanding performances.

Contemporary reviews were moderately positive; over time, however, the album developed a cult following. The band became more well known and started touring more, which negatively affected Mangum, whose mental health began to deteriorate. He eventually withdrew from touring, and Neutral Milk Hotel went on hiatus shortly after. In the years since its release, In the Aeroplane Over the Sea has been described by music journalists as both a landmark album for indie rock and as one of the best albums of the 1990s and its critical standing has risen considerably.