This book presents the abstracts of the 19th International Congress of Heterocyclic Chemistry (19th ICHC) held in Fort Collins, Colorado, 10-15th August 2003 and provides the reader with a topical comprehensive reference source covering the latest developments in the heterocycles area. Each lecture from the 19th ICHC is presented as a one page abstract containing a textual summary of the lecture, including references, figures and contact details of the author(s). Papers are divided into the following sections: heterocyclic natural products, heterocycles in organic synthesis, bioactive heterocycles, heterocyclic materials &related topics, heterocyclic pharmaceuticals. The book of abstracts provides a topical reference source covering the latest developments in the heterocyles area.