The Jesuit Missions to China and Peru were, in their different ways, astonishingly successful, with Catholicism establishing deep roots in Peru, and with the Ming emperors in China giving Jesuits a privileged position at the imperial court, from which position, later, they almost brought about the conversion of the Chinese emperor, and thereby potentially all of China, to Roman Catholic Christianity. This book explores how leading Jesuits, Ricci (1552-1610) in China and Acosta (1540-1600) in Peru, adapted Catholic teaching to fit the prevailing religious outlook and practices in the two countries in order to make Catholicism more understandable and palatable to the local population. It examines in detail Catholic theology, the Jesuit approach to mission, and the concepts which underpinned adaptation, showing in the detail of catechisms produced in each of the territories how adaptation worked out in practice. The book concludes by outlining how the relationship between Catholicism and local culture in the two countries developed.