Iconic images of medieval pilgrims, such as Chaucer's making their laborious way to Canterbury, conjure a distant time when faith was the only refuge of the ill and infirm, and thousands traveled great distances to pray for healing. Why, then, in an age of advanced biotechnology and medicine, do millions still go on pilgrimages? Why do journeys to important religious shrines-such as Lourdes, Compostela, F tima, and Medjugorje-constitute a major industry?...