The breath-based meditation “Kriya-yoga” is a familiar name after its reintroduction by Mahavatara Babaji to Lahidi Mahasaya and subsequent work of Paramahamsa Yogananda in the western world. Though many literatures are available but the lack of clear exposition on the philosophy and practices of this ancient spiritual science is still felt. The book, Kriya-yoga: The Science of Life-force tries to fulfill this want. This work vividly explains “the Knowledge of Life-force” known as Pranauidya, which forms the basis of Kriya-yoga citing from Vedas, Upanisads, Snmad Bhagavadgita Yogasutras of Patanjali and many other ancient scriptures, and analzes how the breath technique quiets the mind, brings. equanimity and results in development of discriminating intelligence that answers the questions and purpose of human life.