A book has a beginning and and end. A story is infinite. When a book begins certain things are accepted as happening before the part you read and as you close the last page of a book you know that as time is ever lasting the story could continue had the author so wished.
So it is with Prelude to Foundation. I thought the Foundation series was a series of three books whose prehistory and future would never be known. It is in fact a series of many. With Prelude to Foundation I got to read about what happened before Foundation and how circumstances conspired for Hari Seldon to develop his theory and start to make it practical. A thoroughly good read.
There was another surprise but first, these are all the books in the Foundation Series (according to the authors introduction to Prelude to Foundation).
Prelude to Foundation
Foundation and Empire
Foundation and Earth
Hooray! now I get to read two more foundation books. I said a "series of many" books, rather than the six listed here. That's because many of Issac Asimov's books are set in the same universe and actually tie together, so rather than be limited to 6 books of the foundation series, the prehistory of Foundation is covered in the "Empire" series of novels and before that the "Robot" series of novels. Indeed, one of the characters from "The Naked Sun" which I read a month or so ago appears in "Prelude to Foundation"! The books before the foundation series are:
The Complete Robot (collection of robot short stories, including the original "I, Robot" short stories from 1950)
The Caves of Steel
The Naked Sun
The Robots of Dawn
Robots and Empire (Last of the Robots Series)
The Currents of Space (First of the Empire Series)
The Stars, Like Dust
Pebble in the Sky (last of the Empire Series)
(foundation series starts)
I can't wait to find the other novels in the second hand bookshops - I think I have an Asimov addiction!