The STAR WARS films are the only primary reference. With the exception of only a few minor points, they are indisputable. This is the explicit policy of the Continuity and Production Editors at Lucasfilm. They are interviewed in STAR WARS Insider #23:
What's 'gospel' and what isn't? 'Gospel,' or canon as we refer to it, includes the screenplays, the films, the radio dramas and the novelisations. These works spin out of George Lucas' original stories, the rest are written by other writers. However, between us, we've read everything, and much of it is taken into account in the overall continuity. The entire catalog of published works comprises a vast history -- with many off-shoots, variations and tangents -- like any other well-developed mythology.
Therefore the films and their adaptations are canon, meaning that they take precedence in essentially all matters. Other forms of unfilmed STAR WARS fiction may be official, meaning that it is subordinate to canon and is required to be consistent with other official works. Issues relating to these secondary sources are described below. Works which do not have the blessing of Lucasfilm Ltd (which is not the same thing as LucasArts) are unofficial and cannot be given consideration.
Like all films, the STAR WARS movies contain errors of a technical nature, which are unrelated to the spirit and substance of the story. Bloopers emerge unexpectedly from the idiosyncracies of the film creation processes. Form the viewpoint of the creators of the film they are unintentional and unwanted. Actually being in the film does not make them a truly "real" part of STAR WARS. In making judgements about the internal reality of the STAR WARS universe I make corrections for the bloopers.
ROTJ badge blooper: A costuming error in Return of the Jedi meant that all Imperial officers had exactly the same rank badge. Moff Jerjerrod and Admiral Piett had the same badges as the most lowly staff officer at the Endor ground bunker. This does not mean that everyone in the film was at the rank of captain or commander! Due to the blooper, where ranks are concerned the Return of the Jedi novel, Galaxy Guide 5 and similar references must be given more consideration than the film itself. For further information read: Imperial Military Insignia.
Secondary and Further Sources.
Where they do not conflict with the spirit or fact of the primary references, other sources are considered. These sources themselves must be sorted according to an order of precedence. First are the film novelisations and the radio dramas. This material is acceptable where it adds to or simply reiterates what is known from the films. Where they conflict with the films they are in error (except in cases where the film has an obvious blooper). Otherwise the secondary source is in error, and cannot serve as a basis for judging the internal reality of the STAR WARS universe. Such materials may be of little worth other than as entertainment.
Jejerrod's last stand. Following orders left by the Emperor, Moff Jerjerrod began rotating his Death Star to destroy the sanctuary moon when the rebels managed to eliminate the security deflector shield. He remained bravely at his command station ready to fire the superlaser while his troops and crew evacuated. This scene is in the novel but for some reason it was cut from the film. The film does not contradict it, and indeed the battle station is seen to have rotated so that it almost points groundward by the time it explodes. Thus this is an acceptable part of the greater continuity.
Next in precedence are most of those materials which are based in the time period spanned by the films. This includes the classic-era products from West End Games, the Williamson Classic STAR WARS comics, several of the republished Devilworlds comics, STAR WARS Holiday Special, the TIE Fighter computer games and Shadows of the Empire.
Length of Executor. The books and journals published by West End Games mention several ships of the same class as Lord Vader's Executor. This is compatible with the films and therefore these vessels can be regarded as part of the proper STAR WARS continuity. However WEG incorrectly state the ships' length as a mere five miles. This conflicts with the films, which clearly and consistently indicate a length of between eleven and twelve miles. Therefore the ships are accepted to exist, but they are much longer than WEG propose. For further information read: Super Star Destroyers and History of the Five-Mile Fallacy.
Following this I rank the stories which are outside the time span of the films but which are of sufficiently limited scope or are otherwise of a nature which does not impinge upon the facts of the universe known in the films. These sources include the Lando Calrissian Trilogy, Han Solo Trilogy and the comic This Crumb for Hire.
Next in precedence are those works of fiction which are set outside the time frame of the movies. Tales of the Jedi comics and all post-Endor novels and comics are included in this category.
Next are those miscellaneous items which have serious or fundamental continuity problems. Here I include Splinter of the Mind's Eye, the North American Marvel comic series and the Droids cartoons and comics. In postings to STAR WARS newsgroups author Andy Mangels has suggested that these stories should be regarded as garbled history, like the delerious dreams of Luke Skywalker when he was in a bacta tank. Some elements of these stories can be sanitised and brought into the fold of respectable STAR WARS but many of the surrounding historical details must be discarded or adjusted.
Droids cartoons and comics: These supposedly are set in a time frame several years prior to A New Hope. However we know that R2-D2 and C-3PO were in the possession of the previous generation of STAR WARS heroes (to be featured in the prequel films). They almost certainly remained continually in the possession of the Skywalker or Organa families between the two generations. The idea that they were somehow lost after Episode III and then reattached themselves to the same crowd of people just before A New Hope strains credulity to breaking point. There are three alternatives: 1.The Droids stories are delusions, distortions or are simply unconnected with the real continuity. 2.These stories really depict events which took place before Episode I. 3.These stories really depict events which will take place after Episode IX. Lady Lumiya: According to the Marvel comics, a one-time romatic interest of Luke Skywalker and apprentice to his father succeeded Lord Vader to become Dark Lady of the Sith. Although it is difficult to fit much of that comic series into the modern STAR WARS continuity, this character has been reintroduced via a Topps card and in a SWRPG article of the STAR WARS Galaxy Magazine. The troublesome peripheral points of continuity surrounding her personal history are left unmentioned, however.
Only reject existing material where absolutely necessary. Story elements must have genuine continuity problems to justify discarding them; material shan't be thrown away simply because many people hold it to be repugnant or embarassing. The STAR WARS Holiday Special is a prime example of this.
Sources should be treated with a view towards unifying everything to give a coherent and concise internal reality to the STAR WARS universe. Wherever phenomena can be explained in several different ways, the theory to be favoured is that which requires the simplest and fewest postulates, and which entails the least ad hoc changes in time. Wherever possible, real physical principles must be applied for the assessment of theories. Common phenomena in technological and natural features of STAR WARS should have common causes.
Rank badges: The Imperial military rank badges of A New Hope and The Empire Strikes Back have some dissimilar characteristics. Some people would choose to ignore one set of badges or the other. Others would glibly assume that the badge system underwent a change during the three years between the films. My approach is to attempt to develop a simple mathematical system which attaches meaning to all of the badges at once, preserving the order of the officers' ranks and bringing everything under one grand unified scheme. For further information see Imperial Military Insignia. STAR WARS Holiday Special: Most of those people who are fortunate (unfortunate?) enough to own videotapes of this 1978 television show wince at their recollection of it. It is generally regarded as insufferably corny. Nevertheless one of the most deeply embarassing aspects of the story, Chewbacca's purile son Lumpy, has been referenced in the modern STAR WARS novel Before the Storm. Perhaps some of the events of the television show are delusional memories of the child Wookiee himself, but it seems clear that Chewbacca's family has become at least as real as the post-Return of the Jedi novels. Try as we might, it really is not possible to find anything in the STAR WARS Holiday Special which conflicts with primary references. Aspects of the show which are less offensive than the Wookiees, like the cartoon encounter between Skywalker and Fett or the discussion between Vader and Bast, are more readily acceptable into the greater STAR WARS continuity. For further information read: The Survival of Colonel Bast, and Boba Fett and the Mandalorians (by Elwyn Chow). Doman Beruss. The Rebel Alliance Sourcebook created a rebel politician from the Corellian system. Corellian characters with this name appear as important New Republic senators in several post-Endor novels, in The Black Fleet Crisis Trilogy and in the X-Wing Rogue Squadron series. Unfortunately Beruss appears as a woman in the earlier story and a man in the later one. I brought this discrepency to the authors' attentions. Subsequently, additional corrective background was created for the male character, making him a human Imperial senator from Illodia. In X-Wing Rogue Squadron: In the Empire's Serivce the Corellian female was explained as belonging to a branch of the Illodian family which migrated to Corellian space. She appears to be an aunt of the younger male Doman Beruss.
However, this debate on what is and is not official Star Wars canon seems to be moot. In a recent interview with the Star Wars Insider 1-800-TRUE-FAN, George Lucas stated that the Prequel Trilogy will profoundly change our perceptions of the current trilogy. Hence, nothing is canon and Lucas is going to change Star Wars history in any way he sees fit in the prequels because, after all, Star Wars belongs solely to him. Stay one with the Force, always . . .