Adapted from SSB

The Spirits' Book
April, 1857 Allan Kardec
April, 1857
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Organized in questions & answers, it is the first book of Spiritism. Containing the Principles of the Spiritist Philosophy on the Immortality of the Soul; The Nature of Spirits and their Relations with the corporeal world; The Moral Laws; The Present Life, the Future life and The Destiny of the Human Races. Its Introduction explains the new ideas and how Kardec organized the 1019 questions and answers contained in the book.
The Mediums' Book
January, 1861 Allan Kardec
January, 1861
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A discussion of the means of communicating with the invisible world, the development of mediumship and the difficulties encountered in the practice of spiritism. Also, the experimental and investigative features of the Spiritist practice are presented, explained and taught.
The Gospel According to Spiritism
April, 1864 Allan Kardec
April, 1864
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The Gospel (Explained under the light of Spiritism) contains the essence of the moral teachings of Christ, thus providing a foundation under which followers of all religions – even those who profess no religion at all – can gather, for it offers a sure guide for our inner transformation, which, according to Christ, is indispensable for us to find future happiness and inner peace, a state that is possible for the spirit on its evolutionary journey to God only by complying fully with the divine laws.
Heaven and Hell
August, 1865 Allan Kardec
August, 1865
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The book is divided into two parts: The first contains a comparative examination of the various doctrines concerning the passage from the earthly life to spirit-life, future rewards and punishments, angels and devils and etc. The second part, which is the result of practical work, is a collection of examples concerning the situation of the soul during and after discarnation. These are testimonies given by repentant criminals, hardened spirits, happy, average and suffering spirits, suicides and spirits undergoing earthly atonements.
Genesis
January, 1868 Allan Kardec
January, 1868
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This is the most scientific book of the codification, it discusses Miracles and Predictions according to Spiritism. It reconciles science and religion and develops a series of important scientific and philosophical topics, relating them to Spiritism.

Find below the 6 workbooks on the main teachings of Spiritism. The educational material was prepared by the Spiritist Society of Baltimore. Although the material can be helpful to anyone, It is mostly for study group meetings.

1 - Introduction to Spiritism
2 - The Spiritist Principles
3 - Moral Laws
4 - Fundamental Principles of the Spiritist Teachings
5A - Fundamental Principles of the Spiritist Teachings
5B - Fundamental Principles of the Spiritist Teachings
6 - Fundamental Principles of the Spiritist Teachings

Source: SSB