Does anyone know the order in which to read Isaac Asimov's Foundation series?

try foundation first. Prelude to foundation should be read later if you enjoy the first book. When in doubt read the book by publish date

There’s no clearly established order, but I agree with Luck… read it in the order of initial publication. That order:

Foundation
Foundation and Empire
Second Foundation
Foundation’s Edge
Foundation and Earth
*
Prelude to Foundation
Forward the Foundation

The alternative, which I also find appealing, is to read all the books in the Foundation universe in their chronological order. That would read like this:

The Complete Robot
The Caves of Steel
The Naked Sun
The Robots of Dawn
Robots and Empire
The Stars, Like Dust
The Currents of Space
Pebble in the Sky
Prelude to Foundation
Forward the Foundation
Foundation
Foundation and Empire
Second Foundation
Foundation’s Edge
Foundation and Earth

However, the Empire books (The Stars, Like Dust, The Currents of Space, Pebble in the Sky) are only tangentially relevant to the main storyline, and I consider Forward the Foundation to be terrible and unworthy of inclusion here—I definitely wouldn’t recommend reading it before the rest of the series. I don’t think Asimov finished that book before he died—my recollection is that it was finished by his wife after his death. In either case, it’s not up to par with the rest of the series, and also contradicts some details of the earlier books.)

The order of initial publication is good because it will let you start in a great spot and read all the way to the chronological end. Then you can go back and fill in the gaps, and they’ll mean more, since you’ll know some of the characters.)

I would read Foundation, Foundation and Empire, and Second Foundation, and stop there. Foundation’s Edge is not terrible, but it was written many years later, and is qualitatively different. Foundation and Earth, Prelude to Foundation, and Forward the Foundation are the result of Asimov trying to tie everything he wrote up into one large tidy chronology; the effort doesn’t work, and the books suffer considerably for it.