The Dungeons & Dragons Rules Cyclopedia is a book that compiles rules from the earlier Basic, Expert, Companion, and Master boxed sets. It covers adventuring from levels 1 to 36. It can be supplemented with the Wrath of the Immortals boxed set, which has rules for adventuring beyond 36th level. Though derived from the earlier Immortals Rules boxed set, the rules in WotI are heavily revised, and this is the primary difference between the RC and BECMI editions. There is also an optional simplified introductory ruleset covering levels 1 through 5, sold in a black box.
Note that some products intended for use with the Rules Cyclopedia were labeled "Challenger Series."
Use this tag to indicate interest specifically in the Rules Cyclopedia version of D&D. Use Classic D&D to indicate broader interest in any version of original or basic D&D, including the Rules Cyclopedia. Use Basic D&D to indicate interest in any version of Classic D&D other than OD&D. You might also want to use BECMI D&D, since many fans consider the Rules Cyclopedia and BECMI rules to be equivalent.