The Book of Souls is the sixteenth studio album by British heavy metal band Iron Maiden, released on 4 September 2015. It is the band's first studio double album, and therefore also their longest to date, with a total length of 92 minutes. In addition to being their longest studio record, it also contains the band's longest song, "Empire of the Clouds", at 18 minutes in length.

The record was a critical and commercial success, receiving positive reviews and topping the album charts in 24 countries. It earned the band their fifth UK No. 1, following 1982's The Number of the Beast, 1988's Seventh Son of a Seventh Son, 1992's Fear of the Dark and 2010's The Final Frontier. In the US, it matched The Final Frontier's success on the Billboard 200, repeating the group's highest placement at no. 4. It also marks the longest gap between studio releases in the group's entire career; at five years, following The Final Frontier.