15th edition of the Britannica. The initial volume with the green spine is the Propædia; the red-spined and black-spined volumes are the Micropædia and the Macropædia, respectively. The last three volumes are the 2002 Book of the Year (black spine) and the two-volume index (cyan spine).
The Encyclopædia Britannica (Latin for "British Encyclopædia"), previously published by Encyclopædia Britannica, Inc., is a popular encyclopædia which since 2011 is published as an online encyclopædia. It is written in British English. It was originally only printed on paper, but late in the 20th century it expanded to have digital, or computer versions as well. Since 2010, it's out of print in paper versions. The encyclopædia is split into many books. The articles in the books are arranged in alphabetical order. There have been versions of it that are for children as well. It is the largest printed encyclopædia in English, and the second largest encyclopædia. The largest is Wikipedia.
The encyclopædia was once very small, the first edition in 1768 only had 3 books. Slowly it became bigger. The last edition, the 15th, started in 1974, has 29 books, plus two indexes. It includes an extra book called Propædia, to classify knowledge. The 29 books and made up of a Macropædia and a Micropædia. The Macropædia is a larger one, with more detailed articles that can be as long as 300 pages, made up of 17 books, while the Micropædia is the smaller one with many much shorter articles that are usually less than 750 words. The Micropædia is used for fast-checking, but for more detailed information, people have to use the Macropædia. Each book is very big, more than 1,000 pages per book. Every year, an update book was published. The last yearbook was for 2018, published in 2017.