This book provides an introduction to the most important philosopher of the Islamic world, Ibn Sīnā, often known in English by his Latinized name Avicenna. After introducing the man and his works, with an overview of the historical context in which he lived, the book devotes chapters to the different areas of Ibn Sīnā's thought. Among the topics covered are his innovations in logic, his theory of the human soul and its powers, the relation between his medical writings and his philosophy, and his metaphysics of existence. Particular attention is given to two famous arguments: his flying man thought experiment and the so-called “demonstration of the truthful,” a proof for the existence of God as the Necessary Existent. A distinctive feature of the book is its attention to the relationship between Ibn Sīnā and Islamic rational theology (kalām): in which we see how Ibn Sīnā responded to this tradition in many areas of his thought. A final chapter looks at Ibn Sīnā's legacy in both the Islamic world and in Latin Christendom. Here Adamson focuses on the critical responses to Ibn Sīnā in subsequent generations by such figures as al-Ghazālī, al-Suhrawardī, and Fakhr al-Dīn al-Rāzī.