This book is an English translation of Book 21 of the Astrologia Gallica, in which Morin sets forth his method of horoscope interpretation. In the first section of the book he reviews the methods of other astrologers and explains why they are insufficient. In the second section he explains his own method, which is both different from and superior to the traditional methods. Morin was a physician who became the most renowned of all French astrologers. He was appointed Royal Mathematician to King Louis XIII and was summoned to be present at the birth of the royal heir, the future King Louis XIV. His master work, the Astrologia Gallica, was published in Paris in 1661. It consists of a Preface and 26 individual books in the scholarly Latin of the 17th century. Many of these Books are now available in English translation, but Book 21 should be read first as it contains the fundamental explanation of the Morin method. Richard S. Baldwin made this English translation directly from the Latin text.