A pocket edition is a small-sized copy of a book intended to fit in one's pocket. Small, pocket-sized variations of books have existed from early times. For example, the early 8th-century gospel book known as the St Cuthbert Gospel has a page size of only 138 by 92 millimetres. However, the concept of producing a specific pocket edition of a book dates to the 20th century. It refers to an edition that has been altered to fit in the reader's pocket, usually by using thinner paper, smaller print, and abbreviation of the text:

When a publisher wishes to produce a pocket edition of a book he can reduce the size of the print, and the thickness of the paper and covers; but he cannot do this indefinitely if the book is to remain legible and serviceable; a time comes when he must also abridge the text, abbreviating of cutting out any appendices or other portions, which, though perhaps interesting in themselves, are not really necessary to the main purpose of the work.