The prior edition of Dungeons & Dragons had only been out a couple of years when Frank Mentzer was tasked with reorganizing the Basic/Expert sets, and lining them up for upcoming releases of the higher-level Companion, Master, and Immortals rules (ergo… “BECMI”).
Also important was adding a “self-teaching” section in the Basic rules. Most players still learned D&D and RPG table play from other players. But TSR regarded this as limiting since the roleplaying game hobby was still small, and potential players might not have access to existing game groups.
The BECMI Basic / Expert box sets don’t lend themselves to a side-by-side format as the earlier B/X edition, but we can still have fun today!
Dungeons & Dragons Basic Rules, Set 1 [BOX SET]
1983, 1989 … Frank Mentzer (editor) … TSR 1011 … ISBN 0880383380
Dungeons & Dragons Expert Rules, Set 2 [BOX SET]
1983 … Frank Mentzer (editor) … TSR 1012 … ISBN 0880383399
This is one large, systemic change in the Expert Rules: all of the human character progressions are slowed down — though usually that’s offered hand-in-hand with some new advantages. So clerics now get fewer spells as they level up, but also have earlier access to sixth level spells; similarly turning is slightly powered down while a new “D+” result is introduced, to destroy more undead than ever. Magic-users also have their spells reduced, while a number of saving throw progressions are dialed back.
Rather remarkably, thieves did not get updated. Their skill progression was unchanged from Cook’s Expert Rules. This may be because Mentzer originally intended to add new skills at higher levels, perhaps in accordance with Zeb Cook’s notes in the Expert Rules, which suggested that higher level thieves might gain “the ability to climb overhangs, upside down, ventriloquism, powers of distraction, and the ability to mimic voices.” That never happened, so when the Companion Rules rolled around, Mentzer realized that thieves didn’t have enough upside. As a result, the thief skill levels were updated after the fact. New, slower skill progressions appeared in the Companion Rules and were then introduced to later printings of Mentzer’s Expert Rules.Much more background info in Shannon Appelcline’s essay at the DriveThru page.
You can see the early/later character ability tables side-by-side at my earlier post:
OK, I actually do have a few Side-by-Side pics of BECMI Basic / Expert
The new Basic Set jettisoned the Keep on the Borderlands module included the earlier B/X edition. Instead, Basic was expanded to have a Players Manual and a Dungeon Masters Rulebook (more later). The Expert box set however, saw fewer changes and retained the Isle of Dread adventure module. The new Expert Rulebook was divided into two distinct parts: Players’ Information and a Dungeon Master’s Section.
Each set has an excellent Index on the back covers!
These sets had long print runs. The first printing was in 1983, and was titled “Basic Rules Set 1.” Later printings switched to “Set 1: Basic Rules” (and likewise for Expert) to conform to the format of the Companion and more advanced sets. The last printing I’ve verified of this Basic set was in 1990(!).
BASIC: Players Manual & Dungeon Masters Rulebook
Module X1: Isle of Dread
(by David Cook and Tom Moldvay)
BECMI gets (mostly) combined into one hardcover: