Philosophers of the thirteenth and fourteenth centuries held that organisms are alive by virtue of possessing a soul, and that the soul endows an organism with various powers. This volume presents a rich selection of key medieval Aristotelian texts on the relation between the soul and its powers, most of them previously untranslated and written by thinkers whose accounts of the soul and its powers are not well known. Each text can be seen as part of a lively medieval debate, responding to or criticizing another text also found in the volume. An introduction situates this debate in its broader medieval context, and the detailed explanatory notes and glossary of terms and arguments make the texts accessible to a wide range of readers including non-experts. The result is a valuable resource for understanding how Aristotle's theory of the soul and its powers was received and transformed in the Middle Ages.