[2] Ned Raggett from AllMusic stated that the singer's "trademark understated drama [are] in full flow" on the "wonderful" song.

[3] Gavin Report wrote, "This is a melodic and harmonic masterpiece with all the elements to make it a classic.

"[4] Music & Media said, "Taken from the motion picture Far and Away, this is the sung version of the original ethereal Clannad instrumental.

"[5] Music Week commented, that Enya's "latest sonic soundscape, Book Of Days, is typically mellifluous.

[6] The Gaelic version of "Book of Days" was used in the theatrical trailer of the Japanese film Calmi Cuori Appassionati (2001).