Book

Books, according to the Tenth Doctor, were the "best weapon[s] in the world." They could be handwritten or printed on sheets of paper made from wood (or a similar material) that were bound together. (TV: Human Nature, Silence in the Library / Forest of the Dead)

Some books were in electronic devices, like The I-Spyder Book of Earth Creatures. (PROSE: The Last Dodo) Thinking books were books that could be read by thought processes. (PROSE: Phoenix)

Books could cover any topic and be intended for entertainment, record keeping, teaching, or other purposes. Diaries were also recorded in books, such as River Song's. (TV: Silence in the Library) Some books were arranged in chapters, which could have titles listed near the front of the book. Some books had afterwards, text written after the main story was concluded. (TV: The Angels Take Manhattan) Another common feature in books was date of publication information. Books could be reprinted, and editions of some books were printed as late as the year 5000000000. (TV: The Unicorn and the Wasp)

By the 51st century, books were somewhat replaced by holovids, direct-to-brain downloads, and fiction mist. According to the Tenth Doctor, however, people still longed the smell of books. (TV: Silence in the Library)

Books were commonly, but not exclusively, stored in a library. (TV: Silence in the Library) The process of producing a book was called writing, and the person who produced the book could be called the author. (TV: The Unquiet Dead, The Angels Take Manhattan)

When the Tenth Doctor and Donna Noble arrived at the Library and were surprised to find that, despite no one being visible, 1,000,000,000,000 life forms were detected there, Donna suggested that the books might be alive. They weren't books, but in fact the Vashta Nerada, who were hatched in the Library's books, using them in place of a forest. (TV: Silence in the Library, Forest of the Dead)

Books as commodity
Books, or rather the information within them, could be valuable.

Cultural relics
The Book of Lies was a rumoured book that detailed the teachings of the Faction Paradox. (PROSE: Unnatural History)

Some books are not just for reading
The Book of the Still was a book used as a rescue device for stranded time-travellers. When the Unnoticed discovered that their existence and location were recorded in this book, they were willing to commit murder to find it. (PROSE: The Book of the Still)

The Doctor and books

 * Also see the TARDIS library.

The Doctor appeared to be fond of books. He has been found reading or shown to be a fan of certain Earth authors in several incarnations. (TV: Doctor Who, The Unquiet Dead, Tooth and Claw)

The Eleventh Doctor was spotted reading the book Melody Malone: Private Detective in Old New York Town aloud to Amy Pond in Central Park. (TV: The Angels Take Manhattan) The Tenth Doctor, while hiding in a library from a lupine wavelength haemovariform, called books the "best weapons in the world." (TV: Tooth and Claw)

Even though he seemed to enjoy reading, the Eleventh Doctor told Amy that he always tore out the last page, so the story didn't have to end. Unlike his successor, however, the Tenth Doctor loved a book with a death at the end, particularly biographies. (TV: The Angels Take Manhattan, Silence in the Library)

There was a library in The Doctor's TARDIS. (PROSE: War of the Daleks, All-Consuming Fire, The Dimension Riders) Its books included Brave New World by Aldous Huxley (PROSE: The Wheel of Ice), Jane's Spaceships (PROSE: War of the Daleks), Every Gallifreyan Child's Pop-Up Book of Nasty Creatures From Other Dimensions (PROSE: All-Consuming Fire), The Time Machine by H. G. Wells (TV: Doctor Who), Robinson Crusoe, (PROSE: Heart of TARDIS) The Murder of Roger Ackroyd by Agatha Christie (signed first printing, with last page missing), War and Peace, The Wonderful Wizard of Oz and The I-Spy Book of British Birds. (AUDIO: Storm Warning)

Science and myth
to be added

Authors
See also a list of writers

Authors were people who wrote books.

Books authored by friends of the Doctor
Summer Falls was a book written by Amelia Williams, former companion of the Eleventh Doctor. Both Artie Maitland and Clara Oswald read it, Clara claiming that Chapter 11 was the best. (TV: The Bells of Saint John)

Amelia's daughter, Melody Malone, wrote Melody Malone: Private Detective in Old New York Town. (TV: The Angels Take Manhattan)

Sarah Jane Smith wrote a book called UNIT: Fighting for Humankind. (TV: Whatever Happened to Sarah Jane?)