So, what does Bethesda define as fallout canon, really?
I guess Fallout 1 & 2 is concidered canon, but what about Fallout Tactics, Brotherhood of Steel and Van Buren?
Furthermore, is the information from the Fallout bible concidered canon?

some of Fallout Tactics, none of BOS... don't know about VB but I'd guess no. We'll have to wait and see what's in the game. I'm sure Ausir is preparing a much more comprehensive answer chock-full-o-links to the wiki.

Fallout 1 and 2 are considered canon. Fallout Tactics is considered partly canon, as in the parts that don't contradict previous Fallouts are more or less canon. Fallout: Brotherhood of Steel is not canon. As for Van Buren, Bethesda neither referenced it nor contradicted it, but it's probably not canon anymore (although since it's not contradicted, you can always include it in your personal canon).

Fallout Bible is considered canon aside from some parts that contradict Fallout and Fallout 2 (there are a few).

This is an article about it in the wiki, although it still requires some work:
http://fallout.wikia.com/wiki/Fallout_canon

I think Van Buren is noncanon because it was never released.

While you're at it. Sort out where Dev quotes and all the promotional material stand.

You're gonna need more boxes then cannon and non-cannon btw.

Well, I generally consider dev quotes about their game canon unless they contradict in-game materials.

Well devs have made some really strange post release explanations...

Do we just interpret dev comments and judge for ourselves?

there is official canon, but it is when it starts contradicting itself it gets confusing.

I know of the official canon. I was talking about when devs start contradicting it.

I listen to canon things inside the game first.

Could you give any examples? I remember there were some strange stuff about how FEV should have caused all the mutations or something.

I remember back when Chris Avellone released the Fallout bibles... So devs contradicting the Fallout canon has been done for a while.

That's actually something the original devs don't agree on. Other examples include the Fallout Bible having the incorrect symbols for BOS and NCR.

and that makes deciding what is canon hard.

Skynet is the biggest example of when Dev's contradict the game

Well, that's a bit different from what I had in mind, since that was Chris Avellone, who was in charge of the Fallout canon at that time, deciding which of the silly pop-cultural references in Fallout 2 shouldn't be considered canon (Skynet's name is too blatant of a Terminator ref). What I was talking about was devs contradicting the games by mistake.

What about devs contradicting the game intentionally? ("This was crap. Actually, it happened this way but we couldn't make it in the game.")
What about devs contradicting other devs?
Black Isle vs. Bethesda?

I still listen to the game or a middly ground. I also listen to the current owner of a series.

Well, most of the information from the devs that I included in the wiki as canon is non-controversial background stuff that does not contradict the game nor other devs. For example, the FO1 manual mentions BADTFL, but I got the full name of the organization only from Chris Taylor:

http://fallout.wikia.com/wiki/BADTFL

Or the history of Tycho, from Jesse Heinig, who designed him:

http://fallout.wikia.com/wiki/Tycho