Rules Cyclopedia

The One Book to Rule Them All?
The Rules Cyclopedia is a compilation of the Basic, Expert, Companion, and Master (BECMI) boxed sets. BECMI was written by Frank Mentzer and became the standard "Basic" game through the 1980s. The first set, simply called "Basic" is often referred to as The Red Box. Released in 1991, the Rules Cyclopedia by Aaron Allston gave the hobby a complete, comprehensive rules book considered by some even today as the best single volume rule book ever.
BECMI was the third version of the basic game to be published by TSR. In 1977 J. Eric Holmes authored the first "Basic" set using White box and its supplements as the basis for the rules. This was around the time Gary Gygax was working on the Advanced game, hence the Basic title for the introductory box set. The Basic book only included rules for characters through third level and it was assumed that by then players would move on to either the White Box or the Advanced game books.
A second edition of the Basic boxed set was written by Tom Moldvay and published in 1980. This was a major revision to the Holmes rules, but was still limited in scope to character levels 1-3. In 1981 the Basic set was followed by an Expert boxed set written by Dave Cook with Steve Marsh and included rules for levels 4-14. Together these sets are often referred to as the B/X Edition.
Basic was revised again in 1983 by Frank Mentzer and it is this edition, together with others in the series, which were compiled and edited to make the Rules Cyclopedia with rules for character levels 1-36. Material from the Immortals boxed set was not included in the Rules Cyclopedia, but was reprinted in a separate product. Release of the 1991 Rules Cyclopedia coincided with a new boxed introductory game titled The New Easy-to-Master Game, but often referred to as the Black Box edition. It included a conventional rule book and a Dungeon Card Learning Pack based on the Science Research Associates (SRA) reading program which had been popular in elementary schools as an independent learning tool. The Black Box came with a two sided color dungeon map and card stand-up characters and monsters and it is the version I used to introduce my then young nephews to the game.
Other than lacking some of the "how to learn the game" material of the boxed sets, the Rules Cyclopedia is a complete game product including referee advice, a detailed setting and monster bestiary. Rules Cyclopedia supports seven character classes, Cleric, Fighter, Magic User, Thief, Dwarf, Elf and Halfling and two optional classes, Druid and Mystic. Fighters can become Paladins, Knights or Avengers and have access to combat maneuvers and weapon mastery giving them more options than in some previous editions of the game.
By 1991 when the Rules Cyclopedia is published TSR has changed hands and with that the focus of the company changed as well. The new target customer age was somewhat younger and the 2nd Edition of the Advanced game had transitioned into a series of supporting rule books and a myriad of official published settings. The Basic game remains as a separate product line, but the reason for this seems obscure. Basic has it's own product line and included in Rules Cyclopedia is material for the planet Mystara, a hollow planet with the surface or Known World setting and the smaller interior or Hollow World setting where adventurers from the Known World may eventually travel.
The first edition of the Advanced game was in print for a decade or more before the second edition arrived. It is interesting to compare the publication timeline of what was variously termed D&D or Basic, etc. with Advanced. Starting with the Holmes Bluebook edition in 1977 Basic was followed just three years later with Tom Moldvay's revision and then three years after that, Frank Mentzer's Red Box. In some ways, the Basic line seems to follow White Box more directly than the Advanced books do. Maybe it is just the continuation of the name, but I also think Basic offers more options for do-it-yourself than Advanced does. In general it presents more as "your game" and less as "the official rules", although the Rules Cyclopedia takes a more authoritative tone than previous editions of "Basic".
I have not run a game using the Rules Cyclopedia, but should I do so, I would referee this game in the same manner I have used while refereeing every RPG since White Box - that is I freely add whatever rules I enjoy (and think my players would enjoy), ignoring the parts of the "official" rules I either don't like, don't want to bother with, or don't recall at the time. I firmly believe part of the enjoyment of RPGs is the freedom to make it up as you go. I am firmly aware this requires fairness on the part of the referee and a trust between players and referee. It works best when I game with friends and is one of the reasons I prefer face-to-face gaming.
The "Basic" and "Advanced" labels disappear with Wizards of the Coast whose own versions of the game differ considerably from either previous line. In the history of the hobby there have been many single volume RPGs, everything one needs in one book, but Rules Cyclopedia is the only one to be an official Dungeons & Dragons product.