The author of the book K. Ingold - a world-famous scientist, the founder of physical organic chemistry - is well known to Soviet (read - Russian) chemists. Published in Russian translation, his book "The Mechanism of Reactions and the Structure of Organic Compounds" (IL, 1959) has long become a bibliographic rarity. The scope of the second edition of this fundamental and well-known monograph has been greatly expanded to include the results of research over the past 15 years. The book examines the mechanisms of essentially all major types of organic reactions, including radical ones, which were not sufficiently covered in the first edition.