This book extensively explores the various influences and connections between Joseph Ratzinger and a number of leading philosophers; engaging with his work by means of Spanish, Portuguese, German, and English schools of thought through the contributions of a global body of scholars. Each chapter in this volume examines precisely how Ratzinger has dealt with the ideas of a particular philosopher, and how he has appropriated their ideas and thoughts. Moving from philosophers he has modified or critiqued – such as Kant, Comte or Wittgenstein – to those who have contributed to his philosophical theology, such as Guardini and Pieper, this truly international endeavour is an extraordinary journey into Ratzinger's engagement with his competing and congenial schools of thought.