American comic book
An American comic book is a periodical which is typically, but not always, 16.83 cm wide by 26 cm tall. It usually has 32 pages, though some special issues can be of greater length.
Most of its content is devoted to a single story. In almost every case, Doctor Who stories told in this format are not concluded in just one issue, but rather are spread out over several issues. It is then typical for the individual issues to be collected in trade paperbacks, where the entire story can be enjoyed by readers.
Sometimes, an American comic book can have both a main story, which takes up most of the book, and a "backup strip", comprised of just a few pages (or even panels) in the back of the book.
As the name implies, the format is popular in the United States and has been rarely, if ever, used as the format of origination in the United Kingdom. Nevertheless, in the 21st century, mainly due to licenses given by BBC Worldwide to both IDW Publishing and Titan Publishing Group, the format has been used to tell a number of Doctor Who stories.
20th century
Though dominantly a format of the 21st century, the first Doctor Who story told in this format was an adaptation of the movie, Dr. Who and the Daleks. At that time in the 1960s, Dell Publishing specialised in publishing adaptations of films and television shows. Daleks was merely one of the hundreds of properties it had obtained the right to publish.
The next major American comic book was Doctor Who (1984), a repackaging of stories from Marvel UK by Marvel Comics Group. Though it had been prefigured by a couple of "pilot" issues in Marvel Premiere, the 1984 series of Doctor Who was the first true "run" of American comic books in Doctor Who history.
21st century
After the successful BBC Wales return of Doctor Who, IDW Publishing picked up the license for American comic books in the waning days of David Tennant's stewardship of the programme on television. They then published a number of stories based on both the Tenth and Eleventh Doctors.
As Peter Capaldi loomed on the horizon, however, the BBC awarded its contract to Titan Publishing Group. Titan then embarked on the most aggressive publication schedule in Doctor Who's American comic book history. As of the latter half of the 2010s, Titan have regular comics with the Eighth through the Twelfth Doctors, as well as specials and limited runs with previous Doctors.