Are all of the Warhammer 40K RPG rule sets compatible? I know that it says Rogue Trader is compatible with Dark Heresy, but what about the others? I would assume so, but want to be sure.

Also, it appears that Dark Heresy is going to have a new rule set. When will this be coming out, and would it be dumb to start purchasing the many books for the 1st edition in light of this pending update?

Thanks in advance for your help.

All five of the current 40K RPG lines are based on a modified version of the 2nd Edition Warhammer Fantasy Roleplay system. That means that at their core, all five 40K RPG use the same system.

However...

Both the power levels of PCs and various subsystems differ drastically across all five lines, so while it is relatively painless for a GM to port bits and pieces back and forth between the lines, the same does in no way apply to player-side stuff.

Going with Dark Heresy and Rogue Trader as an example, the Psychic Powers subsystems the two lines use are incompatible, and a Dark Heresy PC that has spent Experience Points equivalent to a Rogue Trader starting character is significantly more versatile and most likely a fair bit more kick-ass than the Rogue Trader PC (a difference that only increases as the characters rank up).

Every line has similar, very significant, compatibility issues with every other line, and there's no easy or generally applicable way to resolve them. The lines desperately need a unified system.

The 2nd Edition Dark Heresy is in an on-going beta process (or alpha, more accurately) at the moment, but at the time of writing the deadline for the beta has been postponed indefinitely.

The last beta update, let's call it DH2.3b, was a seriously re-vamped and streamlined version of 1st Edition Dark Heresy. It was not at all compatible with any of the 1st Edition 40K RPG lines, and it was carefully set up to not work as an over-all unified RPG system for a number of different game lines. It appears that public reaction to the lack of compatibility both with the existing game lines and with any future game lines or updates of existing ones, is the reason the beta has been postponed indefinitely.

The current plan for the beta is that FFG are hard at work re-writing it into something more in line with Only War (currently the newest and most polished of the 1st Edition 40K RPG lines). When exactly this new beta will materialise is anyone's guess, but I should think fairly soon.

As I started out mentioning, 1st Edition Dark Heresy is actually the 3rd edition of a old and still very popular RPG system, and it isn't radically different from the system it was based on. It's also available right now and has an extensive library of material.

2nd Edition Dark Heresy is - based on the current beta version 2.3 - quite different from anything that came before, so it is quite likely to have more and worse internal issues with things like balance and ease of play than the old edition. It's also not likely to come out this year, and no library of material exists for it.

So... I'd suggest going with 1st Edition Dark Heresy (or another of the five 1st Edition 40K RPG lines), and leaving 2nd Edition Dark Heresy alone until it has been out at least long enough for an errata.

There's a lot of awesome setting material in DH books, but mechanically, they're pretty much obsolete already. It's the big reason for 2e - being the oldest game of the family, DH is horribly lagging behind on rules updates, and previous attempts by authors to sneak new ideas into the rules have had very mixed results - some could argue that current DH isn't even fully compatible with itself.

FFG has this weird approach where they attempt to tighten and improve core rules with each new game, but never issue an errata introducing the same updates to the previous games. The resulting state of compatibility is... hard to convey, actually. I can mix-match stuff from different games with relative ease, but it took time to get used to it and required a certain holistic approach that I'm having trouble explaining.

One thing for sure: never, ever try to do crossover games with characters built using different systems. The balance is all over the place.

Thanks to both for taking the time to respond. That helps a lot. If nothing else, the "old" books are great source material, and fun reading. I will watch for updates on the 2nd edition of DH. It does seem like a "core" rule book with different campaign supplements would be logical, but I have been reading the forums and see that the different power levels of certain character types cause some complexity to that.

Well, the foundation of the rules is common enough that creating a core 40k system is possible. It's just that character generation between systems is done on incompatible principles and thus characters end up on wildly differing power levels despite token exp equivalency.

If you want to mix and match character types from different systems, the best way to go is pick one system as the base, then homebrew an appropriate character option so that it is in line with the careers from that base system. It's actually quite easy once you get the hang of it.