As a rule of thumb, the events that take place within the live-action episodes and movies are canon, or official Star Trek
facts. Story lines, characters, events, stardates, etc. that take place within the fictional novels, video games, the Animated Series
, and the various comic lines have traditionally not
been considered part of the canon. But canon is not something set in stone; even events in some of the movies have been called into question as to whether they should be considered canon! Ultimately, the fans, the writers and the producers may all differ on what is considered canon and the very idea of what is canon has become more fluid, especially as there isn't a single voice or arbiter to decide. Star Trek
creator Gene Roddenberry
was accustomed to making statements about canon, but even he was known to change his mind.
In the publishing world, there used to be two exceptions to the novel rule: the Jeri Taylor- penned books "Mosaic" and "Pathways." Many of the events in these two novels feature background details of the main Star Trek: Voyager characters and were to be considered as references by writers on the show. Now that the show is over, some of those events may never be incorporated into a live action format, so the question of whether details from these novels remain canon is open to interpretation.
With regard to the Animated Series, there are a few details from the episode "Yesteryear," written by D.C. Fontana, that reveal biographical background on Spock and planet Vulcan. Details from this episode have been successfully incorporated into the canon of Star Trek (such as in "The Forge") and now that the Animated Series is out on DVD, we hope that even more can make its way in!