The Society of Jesus is a Catholic religious order of men, whose members are known as Jesuits. It is often recognized by a monogram, IHS, and a motto, AMDG. The former honors the name of Jesus, Jesus who is the savior of the world (Iesus Hominum Salvator). The latter points to the raison d'être of the Jesuits, “For the greater glory of God” (Ad maiorem Dei gloriam). In this introduction and eighteen essays that follow, The Cambridge Companion to the Jesuits focuses principally on the early modern period, from Ignatius of Loyola (1491-1556), founder of the Jesuits, to the suppression of the Society of Jesus in the eighteenth century by Pope Clement XIV. Four of the five parts of the book treat this period: I. Ignatius of Loyola; II. European Foundations of the Jesuits; III. Geographic and Ethnic Frontiers; IV. Arts and Sciences. The last part, Jesuits in the Modern World, examines some key aspects of the Society of Jesus, from its suppression in 1773 and subsequent restoration in 1814, to the present. Ignatius of Loyola was born at the end of the fifteenth century, at Loyola, in the Basque country of Spain. He grew up at a time when Spain was rapidly becoming the dominant power of Europe and indeed of the world. It was also a time of religious change and tension, an age when Spain's monarchs expelled Jews and Muslims, and sought to enforce a kind of uniformity in belief and practice among Catholics. Yet diverse movements, ideas, and practices, old and new, prospered among Spanish Catholics. Lu Ann Homza's essay, the first in this Companion, examines the complexity of the religious culture Ignatius would have experienced in early sixteenth-century Spain.