"The Mediums' Book" is a foundational text in the field of spiritualism, written by the French author Allan Kardec in 1861. The book serves as a guide for understanding the principles of mediumship and the communication between the living and the spirits of the deceased. It outlines various types of mediums and their abilities, as well as the ethical considerations involved in spiritual practices. The work is divided into two main sections: the first focuses on the theory of mediumship, while the second presents practical instructions for aspiring mediums. Kardec emphasizes the importance of discernment and critical thinking when engaging with spiritual phenomena, aiming to provide a structured approach to the study of spiritualism and mediums.