It seems quite natural to explain the activities of human and nonhuman animals by referring to their special faculties. But what are faculties? In what sense are they responsible for a wide range of activities? How can they be individuated? How are they interrelated? And why are different types of faculties assigned to different types of living beings? The six chapters in this book discuss these questions, covering a wide period from Plato up to contemporary debates about faculties as modules of the mind.