Of The Book of Los, which tells essentially the same story of The Book of Urizen from the viewpoint of the mythical character Los, there is but one known surviving copy.

Los, representing the creative imagination opposed to Urizen ("reason"), attempts to give form to a disorganized universe, resulting in the Creation. In Blake's mythology, Los becomes dominated by his counterpart Urizen, the god of reason and materialism. Like Urizen, Los appears in eight of Blake's works, beginning with Europe and The Book of Urizen (both 1794). Described as having a "furious head" and "furious limbs," Los is the child of Enion (representing Lust) and Tharmas (representing the Body) and the father of Orc, who represents Revolution. "Los" may be an inversion of "Sol" (Sun) and thus a source of life.

There are only four engravings for The Book of Los. Shown here are the frontispiece and the title page. The frontispiece shows a crouching and anguished Eno, the Earth Mother, whose name is an anagram of "eon," eternity. The title page indistinctly portrays Los imprisoned in his cavern.