The cultural spiritual heritage of India is both vast as well as rich. The source of this heritage lies in the Great Upanishads. The seers and sages of ancient India, sitting under a tree, in a far-off forest, revealed fundamental principles of perennial philosophy to students who had gone to them with questions of deep and serious inquiry into the very nature of life itself. The Upani-shads contains the essential principles of this perennialageless. The Upanishads contain a large number of inspiring and instructive passages and verses. It has not been possible to include all of them in this book. For the purposes of this book the author has taken those verses and passages that have a bearing on the mystical teaching of the Upanishads. It is mysticism which is the very core of the Upanishads-and so in understanding its mysticism one comes to the heart of the sublime and magnificent teaching of the Upanishads. In this age, where science and technology may lead us into a world devoid of meaning and significance. Modern man needs today a meaningful philosophy if the achievements of science are not to lead him to greater and greater destruction-but to sublime and majestic heights of creative living. It is in the Vision of Life given by the Upanishads that man can find the fundamental philosophy of Creative Living-a philosophy that can serve as a Beacon Light even in the midst of surrounding darkness, a philosophy that can lead him from the unreal to the Real, from darkness to Light, from death to Immortality.