This volume is a collection of the Nobel lectures delivered by the prizewinners in chemistry, together with their biographies, portraits and the presentation speechesat the award ceremonies in Stockholm for the period 1996-2000. Each Nobel lecture is based on the work for which the laureate was awarded the prize. New biographical data of the laureates, since they were awarded the Nobel Prize,are also included. This volume should be of interest to chemists and biochemists, students, teachers and professors of chemistry, and those in related fields. Below is a list of the prizewinners during the period 1996-2000 with a description of the works which they won the prizes for: R.F. Curl, Jr., H.W. Kroto and R.E. Smalley (1996) - for their discovery of fullerenes; P.D. Boyer andJ.E. Walker (1997) - for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP); J.C. Skou (1997) - for the first discovery of an ion-transporting enzyme, Na+, K+-ATPase; W. Kohn (1998) - for his development of the density-functional theory; J.A. Pople (1998) - for his developmentof computational methods in quantum chemistry; A.H. Zewail(1999) - for his studies of the transition states of chemical reactions using femtosecond spectroscopy; A.J. Heeger, G. MacDiarmid and H. Shirakawa (2000) - for the discovery and development of conductive polymers