Some party, usually an editor for the book's publishing company, will go through the text of the book and remove elements, notations, references, narratives, and sometimes entire scenes from a book that could be considered superfluous to the actual story or focus of the book in order to make its audible reading time shorter. A fully abridged audio book can span as little as 4 hours for a book that would span 20 hours unabridged.
The easiest content of a fiction book to edit out is back story often provided for characters or story elements that help support the reality of the story for the reader, but do not provide any narrative to the story itself. For example, a passage such as "John sped away in his automobile, a red 1967 Mustang he'd purchased from a junkyard and spent most of his college years restoring with his father" could be abridged to "John sped away in his automobile, a red 1967 Mustang" or even "John sped away in his car."
In a nonfiction piece, the most commonly abridged details are references, charts, details, and facts that are used to support an author's claim. While it would be unprofessional or irresponsible to omit such details from a book, it is understandable for an audio book as it is assumed the listener wants to hear the author's opinion, and if he/she needs to check the details he/she may refer to the text.
Occasionally, an abridged audio book will be advertised as "Abridgement approved by the author," which would imply that the original work's author has reviewed the trimmed down version of his/her work and agrees that the intention or narrative of his story has not been lost, or that no vital information has been removed.
In many cases, an audio book for a popular title is available in both an abridged and unabridged version, though the abridged version often is released first and almost always costs significantly less than the unabridged version. Often, the two versions are produced independently of each other and may have different narrators. Unabridged versions of books are popular among those with poor eyesight or reading skills who wish to appreciate the entirety of the work, while the abridged version is more often referred by those who just want to follow the story in a quick and entertaining way.
On the radio (for example, in British Radio 4 programmes as Book of the Week, Book at Bedtime, Afternoon Reading, and Go 4 It for children), books are almost always abridged. Because of this, if someone was trying to read along with the book, they would find it much harder than on an audio book.
Sometimes lengthy textbooks are abridged down to a dictionary version, where detailed or explanatory information is removed and only a list of key words from the book and their definitions remain, making the book a companion concordance to the original work.
Abridged print versions of fiction classics are often produced for children, with simplified language; occasionally, material considered potentially inappropriate for children is also removed (a process sometimes called bowdlerization). It is uncommon for abridged versions of fiction books for adults to be published for sale, but it has been done, as with a recent new translation of War and Peace. Reader's Digest, however, is known for their usual practice of printing extremely condensed versions of popular books in their magazine, which is intended to motivate readers to buy the full version of the book. Because of this practice, a common term for a concisely summarized version of a given text or concept is referred to as a "Reader's Digest version," as in "Please give me a Reader's Digest version of your essay," which would be a request to summarize its point as briefly as possible.