Forward the Foundation
is set during Hari Seldon's life, during the time that Psychohistory is being developed and the Foundations are being initiated. I consider Asimov's last novel to be a stellar (!) introduction to the trilogy. The author expertly injects some of the scientific concepts developed since the original Foundation trilogy while staying within the spirit of the grand universe he devised long before writing "Forward". This book offers an outstanding glimpse of how precarious it would be to start a universe-shaking science/technology in a decaying society, as well as an endearing personal portrait of the great Hari Seldon, including his "family" and close colleagues.
If you want the whole Asimov "universe" in story-time sequence, you might want to read the Robot series, the Empire series, and "Prelude to Foundation" before reading this book. Some of those books are of equal stature to "Forward". I consider "Prelude", the immediate predecessor of "Forward", to be of slightly less merit (four and a half stars), though it is well worth reading. I think one could also start the series with "Forward" without being bewildered by the omission of earlier books in the grand series.
Of course, if you want the digest version of the series, the original Foundation trilogy is an amazing work in itself. The trilogy predates word processing and the demand for "tomes", so it is quite concise, and the trilogy is eminently suitable for young readers or for those who want to test the waters before diving in.
If you're a SciFi skeptic, "Forward the Foundation" or the original Foundation trilogy would be great introductions to the field. If you're already a SciFi fan, these are seminal works: entertaining and well worth your time. Enjoy!
The Kindle version of "Forward" is excellent, and reasonably priced, as well.