Asimov is considered one of the Masters of the Science fiction genre. He was a very prolific author, and he started many book series. 3 of the most famous (the robot series, the empire series, and the foundation series) were later merged together in a single epic 15 volume+ series. It is hard to decide in which order to read them. The author himself provided the list of books in chronological order in Prelude to Foundation since the books were not written in the order in which (perhaps) they should be read. I personally do not recommend to read the books in exact chronological order because some of the books that were published at the end were prequels that contains many spoilers. I posted my recommended reading order in [my blog], but I am posting them in chronological order here. I read the entire series, some of the books more than once (first in Italian as a teenager, and then in English as an adult).

Robot Series

The Robot series is a series of 38 science fiction short stories and five novels by American writer Isaac Asimov, featuring positronic robots.Most of Asimov's robot short stories, which he began to write in 1939, are set in the first age of positronic robotics and space exploration. The unique feature of Asimov's robots are the Three Laws of Robotics, hardwired in a robot's positronic brain, with which all robots in his fiction must comply, and which ensure that the robot does not turn against its creators. The stories were not initially conceived as a set, but rather all feature his positronic robots—indeed, there are some inconsistencies among them, especially between the short stories and the novels. They all, however, share a theme of the interaction of humans, robots, and morality.

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The Complete Robot
Isaac Asimov
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The Caves of Steel
Isaac Asimov
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The Naked Sun
Isaac Asimov
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The Robot of Dawn
Isaac Asimov
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Robots and Empire
Isaac Asimov

Galactic Empire Series

The Galactic Empire series (also called the Empire novels or trilogy) is a science fiction sequence of three of Isaac Asimov's earliest novels, and extended by one short story. They are connected by their early place in his published works and chronological placement within his overarching Foundation Universe, set around the rise of Asimov's Galactic Empire, between the Robot and Foundation series to which they were linked in Asimov's later novels.

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Pebble in the Sky
Isaac Asimov
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Blind Alley
Isaac Asimov

Foundation Prequels

More then thirty years after penning the conclusion of the original trilogy, and 5 years after writing two new sequels, Asimov decided to extend the story further and link it with the empire and robot saga. To avoid spoilers, I would read them at least after “Second foundation“, or even better, after “Foundation and Earth”.

Foundation Original Trilogy

The premise of the series is that the mathematician Hari Seldon spent his life developing a branch of mathematics known as psychohistory, a concept of mathematical sociology. Using the laws of mass action, it can predict the future, but only on a large scale. Seldon foresees the imminent fall of the Galactic Empire, which encompasses the entire Milky Way, and a dark age lasting 30,000 years before a second great empire arises. Seldon's calculations also show there is a way to limit this interregnum to just one thousand years. To ensure the more favorable outcome and reduce human misery during the intervening period, Seldon creates the Foundation – a group of talented artisans and engineers positioned at the twinned extreme ends of the galaxy – to preserve and expand on humanity's collective knowledge, and thus become the foundation for the accelerated resurgence of this new galactic empire.

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Foundation
Isaac Asimov
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Second Foundation
Isaac Asimov

Foundation Sequels

More then thirty years after penning the conclusion of the original trilogy, Asimov delighted his fans with 2 sequels!

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Foundation's Edge
Isaac Asimov