Players and Dungeon Masters alike may find that the rules tucked away in the Rules Compendium are organized in a useful way. You'll get more than just rules in this book, though. Behind-the-scenes commentary explains how the rules system has evolved and why certain rules work the way they do, plus you'll have official errata available within the book. Take a look at a few excerpts to see what we mean.
Birth of a Rule
by David Noonan, designer
Take a look at the three core rulebooks. That's almost a thousand pages of rules. So where do they all come from?
We can trace a lot of our rules back to the dim mists of history -- the 1970s, specifically. The most fundamental rules of D&D , such as hit points, AC, and what we used to call the "to hit" rule, all came from those little booklets with storied names: Chainmail; Greyhawk; Blackmoor; Eldritch Wizardry; Gods, Demi-Gods, & Heroes. A lot of D&D 's smaller rules come from those first books too.
Ever wonder why elves are immune to paralysis? As far as we can figure out, that immunity came from a game-balance issue in the original Chainmail rules, which mostly covered medieval warfare (with a fantasy supplement that spawned the game we all play today). Masses of low-cost undead troops were beating up high-cost elf troops, so the "elves are immune to paralysis" emerged as a balancing factor. More than thirty years later, we're still using that rule.
The wellspring of fantasy literature inspired a lot of our rules, too. The Dying Earth books from Jack Vance had some influence on how D&D spellcasting works, although it's not so easy to see the connection today. The salient feature of D&D 's cursed weapons, that you don't want to get rid of them even after you know about the curse, comes straight from Tolkien's One Ring and Moorcock's Stormbringer.
WHAT GIVES BIRTH TO RULES TODAY?
Essentially, my job is to sit at this desk and crank out new rules for you. So where do I come up with new rules?
Trouble at the Table: If I see something that isn't working at my D&D table, a new rule is often the solution. Most of our rules for polymorph and similar effects fall into that category. We created the stacking rules for D&D bonuses to help solve the confusion at the table when nobody knew which bonuses combined well with which other bonuses. It helped us with some game balance issues too, because unlimited stacking is a key ingredient in some way-too-good character builds.
Extension of Another Rule: New rules tend to percolate through the system naturally. Once you've got a rule that lets a sorcerer change his "spells known" list, it makes a certain amount of sense to come up with a parallel rule for a warlock changing his "invocations known" list.
New Blood: When you're seizing new territory for the game, of course it's going to give birth to a lot of new rules. The psionics rules are a good example of new territory for D&D -- although it's territory that we reclaim with each new edition of the game. And the rules we create for psionics sometimes lead us to extend other rules. Once we used swift actions and immediate actions in Expanded Psionics Handbook, we started extending them all over the place.
Thin Air: Sometimes new rules just come to a game designer unbidden. Game design is like any other creative endeavor in that respect.