The Medium's Book was the second book of the Codification of the Spiritist Doctrine, first published in 1861. Composed of 32 chapters, the book is devided into 2 main parts.

The first is an overview of Spiritism, and a discussion of the many theories used against spiritism and their many inconsistancies.

The second part is a detailed classification of paranormal phenomena, with a focus on those capable of communicating messages, and thorough descriptions of the mechanisms that are involved. It also contains serious warnings against unguided use of the gift of mediumship, especially without the necessary seriousness. This book helps clarify why mediumship is an incredible gift, but also a tough responsability that can easily be abused.