Jacques Le Goff, The Birth of Purgatory (1984, reissued 1990; originally published in French, 1981), is the most focused treatment of Western Christian beliefs about purgatory. Jean-Claude Schmitt, Ghosts in the Middle Ages: The Living and the Dead in Medieval Society (1998; originally published in French, 1994) traces the connection between ghosts, dreams, and purgatory in medieval culture. Stephen Greenblatt, Hamlet in Purgatory (2001), studies the history of purgatory in England and its survivals and echoes in Shakespeare’s plays, above all Hamlet.
Purgatory in medieval vision literature is examined in Robert Easting (ed.), St. Patrick’s Purgatory (1991); Eileen Gardiner (ed.), Visions of Heaven and Hell Before Dante (1989); Michael Haren and Yolande de Pontfarcy (eds.), The Medieval Pilgrimage to St Patrick’s Purgatory: Lough Derg and the European Tradition (1988); Takami Matsuda, Death and Purgatory in Middle English Didactic Poetry (1997); Alison Morgan, Dante and the Medieval Other World (1990); Howard Rollin Patch, The Other World, According to Descriptions in Medieval Literature (1950, reissued 1970); and Carol Zaleski, Otherworld Journeys: Accounts of Near-Death Experience in Medieval and Modern Times (1987).
The idea of purgatory in Chinese traditions is best discussed in Stephen F. Teiser, The Scripture on the Ten Kings and the Making of Purgatory in Medieval Chinese Buddhism (1994, reissued 2003); and Arthur P. Wolf (ed.), Religion and Ritual in Chinese Society (1974).