This book is a thorough commentary on the original text by Maharishi Swatmarama. It elucidates the entire science of hatha yoga as it was conceived and practised, not for health and fitness only, but for awakening the pranas, chakras and kundalini shakti. This text points out that hatha yoga is not just a physical practice but a process of cellular transmutation from gross, to subtle to divine. Thus hatha yoga was considered the foundation of all higher yogas. This text clearly shows the link between tantra and hatha yoga, and also emphasises that hatha yoga leads to raja yoga, otherwise it is practised in vain.