Ray Tracing Gems, a book with the goal of educating developers at all levels about important concepts and the state of the art in ray tracing, is due to be released mid-March in hardback form, but the contents are being made available at no cost as the chapters reached a finished state in the weeks leading up to the hardbook release.

Today NVIDIA Developer Zone posted Part II of the book here. Keep an eye on the book's page as the schedule shows new parts released every few days until February 25, 2019.