I refer to the theoretical assessment of probabilities concerning the future as ‘psychohistory.’Isaac Asimov’s Prelude to Foundation is both a prequel and a sequel to the first five books in the Foundation Series. Chronologically, the actions take place before the first book, Foundation. Informationally, the storyline builds on the details that were revealed in the previous books, including the last one, Foundation and Earth. Not only is Prelude to Foundation an interesting story about how Hari Seldon began to develop psychohistory, but it also addresses some of the questions raised about Earth, the early days of human expansion into the Galaxy, and even Gaia. This made the book doubly fulfilling for me. Briefly, after Hari Sheldon introduces the theory of psychohistory at a mathematics conference on Trantor, his life is forever changed. The Emperor and his rival want to use Sheldon as a tool for propaganda. If they can’t use him, they want to destroy him. Hari finds that in order to protect himself, he must flee to the parts of Trantor where he will be safe. He finds a benefactor in the mysterious Chetter Hummin, a reporter with powerful connections all over Trantor. Hummin tells Sheldon that the Empire is in decay and that psychohistory might be a way of helping humanity. Sheldon soon meets Dors Venabili, a history scholar. She becomes a partner and a bodyguard to Sheldon as he travels around Trantor and tries to find a way to transform psychohistory from a theory into a practical tool. In each of the areas that they visit, Sheldon seems to get himself into some sort of trouble. After being disappointed with Foundation and Earth, I was very satisfied with Prelude to Foundation. Intellectually, I have been curious about psychohistory since Foundation and had a drive to know more. But Prelude to Foundation is also a good story. Sheldon is an interesting, likeable character with good integrity. Each of the areas that Dors and Sheldon visit is well thought out and helps Sheldon to grow. Also, Asimov takes on such topics as selective history, prejudice, taboos, power, and tradition. The book is the complete package.