Chronology, Continuity & Canon are the eternal obsessions of fans of all TV shows, not just fans of Doctor Who. At its simplest, when something is established we don't like it when it's subsequently contradicted. We like to know the exact order when things happen and we pay attention when characters mention things we haven't seen on TV. It has always been part of the fictional reality of Doctor Who that the characters have a life beyond what we see them doing on TV. The inference is that the adventures we see the Doctor having on TV aren't the only ones he has. Question is, what are those adventures and when do they take place? And before you know it, you're off and playing Hunt The Story Gap, trying to track down the places where those non-TV adventures happened. Cue that other eternal hallmark of the fan - The List.

For the TV stories, it's usually the case that Production Order and Transmission Order are the same, so the order you see them in on telly is pretty much the order they happened to the Doctor, though there have been exceptions over the years. With the Big Finish audios, arguably Canon since The Night Of The Doctor, it's not always so easy to know where a particular story takes place. I call it Minding The Gaps. In general I adhere to the primacy principle, so if Story A is released before Story B, and they both go in the same Story Gap, then Story A goes in first unless there is clear evidence to the contrary.

The Big Finish audios have to take place in the Story Gaps between television adventures, which are the Primary Texts of Doctor Who. Audio adventures, original novels and comic strips are all Secondary Texts. So, when it comes to continuity, the general principle is that the Primary Text takes precedence unless there's a compelling reason not to adhere to it - The Primacy Principle. If it's clear that there is a run of consecutive adventures taking place then the same rules apply as on Television: if A is released before B, then A takes place before B, unless there is a compelling reason for it not to.

I call this the rule of Chronological Sequentialism. But for every rule, there are always exceptions. For instance, take the audio Helicon Prime - the story has Jamie relating how Victoria is away on her graphology studies, which is clearly a nod to the infamous Season 6B, which doesn't take place in this timeline, only in the timeline for the "JNT Universe" of the Sixth Doctor. As a result I've ignored the story altogether but you could easily retcon it to have Jamie confused due to the lightning strike if you wanted to...

There are instances where the end of one story clearly leads straight into the start of another. Like The Dominators into The Mind Robber for instance. Or what about the run of four consecutive stories early on, where we go all the way from The Highlanders to The Macra Terror before we get a Story Gap that Big Finish can slot their "Ben, Polly & Jamie" audios into. For other stories it's implied that the end of one story leads into the start of another but it's less clear cut. For instance there could be a Story Gap in between the end of The Enemy of The World and the start of The Web of Fear but it's not clear how much time has passed since Salamander got sucked out of the TARDIS, so the continuity jury is out on that one. It's sheer common sense as to where the gaps are, be they obvious or implied & inferred.

So in drawing up this chronology, I've only gone by what I've actually heard when listening to the audio when working out where a particular story appears in the Doctor's timeline. Just because a CD release for a particular story says it takes place between two stories that doesn't mean I'll agree with it - I'll listen and come to my own conclusions based only on what I've heard.

Of course, some placements are inevitably arbitrary as there is no clear guide as to where they go. In those cases I've just picked a spot where it seems to me that it might fit and isn't too similar to the stories around it. In some cases I've also come up with what I like to call The Untold Adventures, to cover those Story Gaps where adventures may well have taken place but Big Finish haven't plugged them yet. For instance, the other adventures the Doctor, Ben & Polly may have had before Scotland in 1745.

You'll notice that I haven't placed either The Three Doctors or The Five Doctors. There are two reasons for that. The first is that those adventures don't take place in this timeline, only in the timelines of the Universes of the Doctors Three and Five. The second is that there's so little to go on that you could place them anywhere you like and nobody could argue with it, rendering the exercise pretty pointless.