The diaries of Clara Mary Jane Clairmont are, so far as is known, the last of the major documents of the Shelley-Byron circle to be published. Only the writings of the Shelleys themselves surpass hers in importance for those interested in the careers of the poets and their friends. Best known as Byron's mistress and the mother of his daughter Allegra, "Claire," as she preferred to be called, is important to literary history for her role in bringing Byron and Shelley together.

Claire Clairmont began her journals in 1814, when she accompanied Shelley and her half-sister,...