Book

Books, according to the Tenth Doctor, were the "best weapons in the world." (TV: Tooth and Claw) 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) Some books from Gallifrey, including Encyclopedia Gallifreya, were in liquid form, and were kept in bottles. (TV: Journey to the Centre of the TARDIS)

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 afterwords, 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 for the smell of books. (TV: Silence in the Library)

Indeed, even as technology progressed, paper books proved more affordable to produce and to distribute, and therefore more accessible. This format was also a better long-term archiving strategy than computer storage, standing the test of time. Into the Analog Wars, no other format truly replaced books. (AUDIO: The Black Hole)

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. (TV: Silence in the Library) 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: Forest of the Dead)

Books as commodity
Books, and often the information within them, could be valuable. First-edition copies, in particular, were worth a great amount, (AUDIO: The Crooked Man) and some books were sought after for their historical or religious significance, and indeed their rarity. (AUDIO: The Book of Kells)

For this reason, it was not uncommon to have valuable books stolen, (AUDIO: The Book of Kells, The Crooked Man, COMIC: Voyager) and even second-hand book shops were equipped to keep such volumes under lock and key. (AUDIO: The Crooked Man)

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 Crooked Man, from the Land of Fiction, killed Celia Turner by breaking the spine of the book she came from, Hearts and Minds 2: Turner's Revenge. (AUDIO: The Crooked Man)

The Doctor and books
The Doctor appeared to be fond of books. He was a fan of certain Earth authors in several incarnations. (TV: Doctor Who, The Unquiet Dead, Tooth and Claw et al.) The Time Lord was capable of reading a book in seconds, simply by flipping through its pages. (TV: City of Death, The Time of Angels, Rose, AUDIO: Invaders from Mars)

The War Doctor listed books among the things he wanted to teach his companion Cinder about. (PROSE: Engines of War) 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) The Eleventh Doctor read the book Melody Malone: Private Detective in Old New York Town aloud to Amy Pond in Central Park. (TV: The Angels Take Manhattan)

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. (TV: The Angels Take Manhattan) Unlike his successor, however, the Tenth Doctor loved a book with a death at the end, particularly biographies. (TV: Silence in the Library) The Tenth Doctor in fact specifically protested about his copy of Agatha Christie's The Murder of Roger Ackroyd missing the last page. (TV: The Unicorn and the Wasp)

There was a library in the Doctor's TARDIS. (PROSE: War of the Daleks, All-Consuming Fire, The Dimension Riders, Journey to the Centre of the TARDIS) Its books included Brave New World by Aldous Huxley, Jane's Spaceships, Every Gallifreyan Child's Pop-Up Book of Nasty Creatures From Other Dimensions, The Time Machine by H. G. Wells, Robinson Crusoe, 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. (PROSE: The Wheel of Ice, War of the Daleks, All-Consuming Fire, Heart of TARDIS, The Last Dodo, TV: Doctor Who, AUDIO: Storm Warning)

It also included books from his home world, specifically The History of the Time War and the Encyclopedia Gallifreya. (TV: Journey to the Centre of the TARDIS) The Doctor also possessed a printed edition of Christie's Death in the Clouds published in the aforementioned year 5000000000. (TV: The Unicorn and the Wasp)

Books to teach other subjects
The Fourth Doctor learned Tibetan from Teach Yourself Tibetan, a book he read on Chloris to better understand Everest in Easy Stages, which was written in that language. (TV: The Creature from the Pit)

Books authored by friends of the Doctor
Bernice Summerfield was the author of Down Among the Dead Men (PROSE: Oh No It Isn't!, Dry Pilgrimage, Walking to Babylon) and Down Among the Dead Men Again, (PROSE: Seeing I, AUDIO: Buried Treasures) while her husband wrote pieces of xenopornography such as Nights of the Perfumed Tentacle. (PROSE: Beige Planet Mars, Sex Secrets of the Robot Replicants)

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) Night Thief of Ill-Harbour was another famous book written by Amelia Williams. (PROSE: Summer Falls and Other Stories)

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?)