A very up to date work that is divided into three chapters. The first chapter contains dialogues between Kardec and a critic, a skeptic and a priest, providing answers to questions of those who don't know the basic principles of Spiritism. The second one presents topics of practical and experimental science, in a kind of summary of The Mediums' Book. In the third part, there is synthesis of The Spirits' Book, with the solutions according to the Spiritist Doctrine to psychological, moral and philosophical problems. Finally, there is a biography of Allan Kardec, written by Henri Sausse.