Encyclopædia Britannica
There are 15 official editions of the encyclopædia, with some extensions to the 3rd and 5th editions (see the Table below). Actually, one can say that the 10th edition was only an extension to the 9th edition, and the 12th and 13th editions were extensions to the 11th edition. The 15th edition was reorganised in 1985, and the updated, current version is the 15th edition.