Spiritual knowledge is the supreme among all types of knowledge. The shruti says 'Advaita Darshnam Jnanam'. Vision of non-duality is true knowledge. The Upanishads have revealed this non-dual knowledge which is to be awakened through the process of Shravanam (listening), Mananam (reflecting) and Nithidhyasanam (meditation). This book presents the doctrine of Upanishad (Upanishad Matam) in a very rational and lucid manner in the perspective of modern thought. A holistic approach has been adopted for the intuitive realisation of the Self. Many important subjects like Chastity, Meditation, Vijnana, Prajnana, Sanjnana, and Samyak Jnana have been dealt with in this book. The result of spiritual knowledge is withdrawal from the unreal world and the attainment of absolut satisfaction. This book concludes its exposition on spiritual knowledge by highlighting the necessity of Monasticism for constant abidance in the non-dual Self-awareness.