The Mediums' Book is the logical continuation of Allan Kardec's first volume, The Spirits' Book. If the latter establishes the theoretical foundations of the doctrine, The Mediums' Book deals with its practical aspects. Throughout this book, the author draws a link between the theoretical and experimental aspects of mediumistic faculties, and invites us to follow this practice in detail with highly qualified beings.
The Mediums' Book, which deals with natural and supernatural faculties, comprises two parts. In the first part, Allan Kardec reviews the Preliminary Notions of the Spirit World, deals with the existence of Spirits, the Supernatural and the Marvelous, the method of proceeding with the Materialists and the Skeptics, as well as the Systems.
The second part deals with Spiritual Manifestations and constitutes the analysis and the experimentality of the Spiritist Method of Knowledge and Communication whose foundation lies in the Mediumship Faculty of the Human Being.
The Mediums' Book contains the Special Teaching of Spirits on the Theory of all kinds of Manifestations, Means of Communicating with the Invisible World, Development of Mediumship, Difficulties and Pitfalls that can be encountered in the Practice of Spiritism.