Book of Days is the eleventh studio album by the progressive rock band Nektar, released in 2008. It was preceded by the departures of keyboardist Alan "Taff" Freeman, who up until this point had been the only member of Nektar to appear on all of their albums, and bassist Randy Dembo. Two original band members, guitarist/frontman Roye Albrighton and drummer Ron Howden, were joined by keyboardist Steve Mattern, bassist Desha Dunnahoe, and guitarist Steve Adams.
For the deluxe release, Albrighton's solo album The Follies of Rupert Treacle was included.