This book represents an exceptional example of dialogue between Faith and Science. Over the course of nine years, from 2013 to today, Pope Emeritus Benedict XVI and Piergiorgio Odifreddi, an atheist mathematician, met several times in person and maintained an intense and profound epistolary correspondence. Everything is documented in these pages: Odifreddi recounts their conversations in detail and the letters are reported in full. It is a formidable spiritual journey, in which the theologian and the man of science discuss countless themes: ethics, anthropology, spirituality, the "ultimate" questions on life and death, love and pain... It flows, in these pages, a "surprising crowd of authors", as Cardinal Ravasi defines it, from Pseudo-Dionysius to Dostoevsky, from Hildegard of Bingen to Küng, from Guardini to Sartre, from Thomas Mann to Amartya Sen, from Jan Assmann to Coetzee, and so on, while in the field of science John Nash and Kurt Gödel stand out. However, there is yet another element that makes this long dialogue unique: despite having diametrically opposed positions, Odifreddi and Benedict XVI recognize the common goal of the tension to understand, of the search for the Truth. An aim that stimulates their conversations, making them intimate, arouses autobiographical memories in both and gives birth to an undoubted complicity.