Oh let me think, the tree I've done which were written as a trilogy and then there are a couple of prequels and sequels written afterwards that aren't that great, and then there are the ones not written by the original author...
"prelude..." "forward the..." "foundation" "...and empre" "second..." "the edges of the..." "...and earth"
but these are another books from Asimov, and from the same universe, but these are previously to foundation series, there are called "the robot series" and "the triptic of the empire"
"forward the..."
"foundation"
"...and empre"
"second..."
"the edges of the..."
"...and earth"
but these are another books from Asimov, and from the same universe, but these are previously to foundation series, there are called "the robot series" and "the triptic of the empire"