Established in 1960, Advances in Heterocyclic Chemistry is the definitive serial in the area — one of great importance to organic chemists, polymer chemists, and many biological scientists. Written by established authorities in the field, the comprehensive reviews combine descriptive chemistry and mechanistic insight to yield an understanding of how the chemistry drives the properties. Degenerate ring transformations of heterocycles are classified as reactions in which a heterocyclic system is converted into the same heterocyclic system. This monograph covers an authoritative, comprehensive overview of a host of degenerate ring transformations in five- and six-membered heterocycles. It shows how by the use of 15 N-labeled, 13 C-labeled, or selectively substituted compounds these degenerate rign transformations can be discovered and how most of the results can be explained by the Addition Nucleophile, Ring Opening, and Ring Closure [ANRORC] mechanism. Another main topic of the monograph is the occurrence of degenerate ring transformations.