Bibliomancy is divination by means of a book: a sacred or otherwise authoritative text is opened at random (or to a randomly chosen line), and the passage lit upon is read as guidance, omen, or answer to a question. The practice depends on treating a particular text as so charged with truth or divine presence that even a chance encounter with it must be meaningful. Its history is closely tied to the most revered books of each culture. In the classical world the poems of Virgil were used this way, the sortes Virgilianae, as, earlier, were the Homeric epics.
In Christian Europe the Bible was the usual instrument (the sortes sanctorum or sortes biblicae), a practice both widely used and repeatedly condemned by church authorities wary of treating scripture as a lottery; a famous instance is Augustine's conversion in the garden, prompted by opening Paul's letters at random.
Comparable practices attach to the Quran and to the poetry of Hafez in the Persian world (fal-e Hafez), and the Chinese I Ching functions on a related principle. Bibliomancy reflects a recurring conviction across traditions: that a supremely authoritative text contains an answer for every situation, and that the moment of opening it can be guided, by God, fate, or chance rightly read, to the passage one needs.