In the Introduction, Aleister Crowley, who translated the book, called it the masterpiece of Levi. The author, Eliphas Levi, reveals how to use the most hidden of occult secrets to reach the highest order of the human mind. The author has determined that the key to the world's mysteries resides on a higher plane that can only be accessed by reconciling the contradictions found in the dualism of reality. The methods used to accomplish this are explained as being this key. One may discover in this book the absolute knowledge of good and evil, why alchemy is the daughter of the Qabalah, secrets of life and death, the astral world, and the deeper mysteries of religion, including the Christian Cross. It also covers the use of Spiritualism, the Tarot, mesmerism, mediumship, magnetic powers, and various forms of magic that may be used to invoke either angels or demons. Eliphas Levi is legendary in the field of the occult, transcendental magic and the hidden world. If this book is indeed his masterpiece, it should leave no question in the minds of readers regarding its ability to live up to its title -- the key of the mysteries.