The Bishoujo Senshi Sailor Moon Gengashuu [officially translated as “Pretty Soldier Sailor Moon Original Picture Collection”] are artbooks which reprint the color illustrations drawn by Naoko Takeuchi during each year of the Sailor Moon manga. These artbooks have been out of print for many years; if you look for copies second-hand on eBay, be aware that there are many bootleg versions.
Below is a full set of scans from my personal copy of the original Japanese edition. Some of the two-page spreads have been edited together by fans who sent them in to me; I have also included scans of the illustrations as they were reprinted in the manga.
Visit this page for translations of the liner notes printed in the back of the book.