Advances in Heterocyclic Chemistry, Volume 126, is the definitive series in the field, one that is of great importance to organic chemists, polymer chemists and many biological scientists. Because biology and organic chemistry increasingly intersect, the associated nomenclature is used more frequently in explanations. Updates to this release include sections on The Literature of Heterocyclic Chemistry, Part XVI, 2016, The preparation and properties of heteroarylazulenes and hetero-fused azulenes, Recent developments in pyrazole chemistry, Yne, Ene-Yne Synthetic Approaches to Heterocycles, Appel Salt and Heterocycles: A review of Thirty Years of 4,5-Dichloro-1,2,3-dithiazolium Chloride Chemistry, and more. Written by established authorities in the field, this comprehensive review combines descriptive synthetic chemistry and mechanistic insight to yield an understanding on how chemistry drives the preparation and useful properties of heterocyclic compounds.