This book summarizes and records the recent notable advances in diverse topics in organic crystal chemistry, which has made substantial progress along with the rapid development of a variety of analysis and measurement techniques for solid organic materials. This review book is one of the volumes that are published periodically on this theme. The previous volume, published in 2015, systematically summarized the remarkable progress in assorted topics of organic crystal chemistry using organic solids and organic–inorganic hybrid materials during the previous 5 years, and it has been widely read. The present volume also shows the progress of organic solid chemistry in the last 5 years, with contributions mainly by invited members of the Division of Organic Crystal Chemistry of the Chemical Society of Japan (CSJ), together with prominent invited authors from countries other than Japan.