This is the nineteenth annual volume of "Progress in Heterocyclic Chemistry", which covers the literature published during 2006. As with previous volumes in the series, Volume 19 will enable the reader to keep abreast of developments in heterocyclic chemistry in an effortless way. It provides a critical review of the heterocyclic literature published during 2006. It presents specialized reviews. It includes chapters that are written by leading researchers in their field.