The eighteenth annual volume of "Progress in Heterocyclic Chemistry" covers the literature published during 2005 on most of the important heterocyclic ring systems. This volume opens with two specialized reviews. The first, by Heui-Yeon Kim and Cheon-Gyu Cho covers 'The Diels-Alder cycloadditions of 3,5-dibromo-2-pyrone and its derivatives'. The second, by Jean-Luc Girardet and Stanley Lang discusses 'Recent developments in the chemistry of nucleosides'. The remaining chapters examine the 2005 literature on the common heterocycles in order of increasing ring size and the heteroatoms present. References are incorporated into the text using the journal codes adopted by "Comprehensive Heterocyclic Chemistry", and are listed in full at the end of each chapter. Included in the index are systematic heterocyclic ring system names. This book includes new contributions from experts in the field.