I am collaborating with Alekh Agarwal (MSR), Sham Kakade (UW), and Wen Sun (Cornell) on a monograph on RL theory. The monograph started with my 598 course notes as of F18/S19, and has been substantially expanded and enriched since then by my coauthors (with some minor contribution from my side). The notes are being actively updated, and any feedback is welcome.