The Yoga Sutras is a codification of the essence of Yoga practice and is considered the foundational text of modern Yoga. Patanjali walks the student through the basics of yoga, from it’s simplest definition (“yoga is ceasing the modifications of the mind”), to the preliminary ethical practices (yama & niyama), through the essential points on concentration and meditation, and on to the pinnacle of yoga practice: kaivalya, “spiritual isolation,” or what we might rather call “unification” or “oneness,” liberation from the sense of separateness.
While often studied in isolation, the Yoga Sutras do not and cannot stand alone and apart from the rest of Indian spiritual philosophy. They rest upon and assume, for instance, a knowledge of many aspects of the Samkhya and Vedanta traditions. As noted by Charles Johnston, “Patanjali plunges at once into the middle of the most practical psychology, assuming in his readers a knowledge of the spiritual philosophy of ancient India.” Students are recommended to study the Upanishads, Sankhya and Vedanta texts, and texts like the Bhagavad Gita as preliminaries to a study and attempted practice of Patanjali’s system.
The Yoga-system of Patanjali, called Yoga-sutras, and the Yoga-bhashya of Veda-Vyasa by James Haughton Woods
The Sutras of Patanjali with the Bhashya of Vyasa by Ganganatha Jha