The purpose of this book is to present a systematic discussion of the philosophy of classical Yoga as an interpretation and further elucidation of the philosophy of classical Samkhya, based upon new translations into English of the three most important texts of philosophical Yoga, namely, the Yoga-sutra-s, attributed to a certain Patanjali and usually called the Patanjala-yoga-sutra or Patanjala-yoga-sastra (hereafter simply YS) (ca. CE 350-450); its basic commentary (the Bhasya) attributed to the legendary Vedavyasa (hereafter the VB) (likewise ca. CE 350-450); and a long sub-commentary called a Tika (or Vyakhya) entitled Tattvavaisaradi ("A Skilled Clarification of the Truth") (of Yoga) (hereafter TV) composed by the well known scholar of Indian philosophy, Vacaspatimisra (hereafter VM) (ca. CE 950).