The author offers a systematic exposition of Patañjali’s Yoga-sūtra as interpreted by classical commentators, tracing its metaphysical and psychological foundations and its affinities with Sāṃkhya thought. The first part examines core categories such as prakṛti and puruṣa, the reality of the external world, and the process and stages of evolution and change; the second treats moral psychology, the theory of karma, ethical questions, and the practices and stages of attainment including the yogāṅgas and samādhi. The focus remains on theoretical, cosmological, and doctrinal clarification rather than on giving practical instruction, with attention to key commentarial debates.