Marvels of the Heart is a classic Sufi manual on the `science of the heart.' For Sufis, the heart is more than a physical organ, it is the seat of the soul, which holds the key to the intimate relationship that exists between the body and spirit. Each heart, according to traditional wisdom accumulated over centuries of spiritual practice, possesses four qualities: predatory, animal, demonic, and angelic. The latter represents one's true origin and potential, and through the proper use of the intellect and by engaging in spiritual practices, one can restore equilibrium to his inner core. As the Qur'an says: By the remembrance of God do hearts find peace. Abu Hamid al-Ghazali (d. 1111) was the leading jurist, theologian, and mystic of premodern Islam, and remains its truest advocate in modern times. As a teacher of Sufi initiates he recorded these practical teachings in his four-volume compendium of spiritual knowledge, the Thya' `ulum al-din (The Revival of the Religious Sciences), from which the present work---Book 21---is taken. Imam al-Ghazali uses a series of traditional Sufi teachings and stories to illustrate the theme of the heart as a mirror. The light of the divine can only shine in the heart when the seeker recalls the Prophet's teaching that "everything has a polish, and the polish of hearts is the remembrance of God." Base character traits that accumulate when the true nature of the heart is neglected are like "a smoke that clouds the heart's mirror"; rust corrodes the hearts of all but those who polish them by the remembrance of God. Hearts thus illuminated lead one to success in this life and eternal salvation in the next. Originally translated for a PhD thesis in 1938 as "The Religious Psychology of al-Ghazzali," for years this translation was only available to researchers and cognoscenti. Fons Vitae is proud to offer the complete text to the general public and specialists alike.