In the twelfth century, a French poet wrote a verse romance about a young knight who witnesses a mysterious procession centered on a radiant vessel, a "grail." Left unfinished, the poem inspired other writers of prose and verse, until the story was completely rewritten into the Arthurian romances, in which the vessel becomes a relic of the Last Supper, the Holy Grail. For hundreds of years, the Grail story has haunted the western imagination. But the original medieval texts are full of inconsistencies, as different writers attempted to complete the story in varied ways. This encyclopedia illuminates a path through the Perilous Forest of literature and legend. Entries summarize the stories of the principal characters, sacred objects and places associated with the Grail. An Afterword shows how mysteries of the grail continue to enchant the scholars and creative writers who have transformed the medieval legend into modern mythology.