This volume is a collection of the Nobel lectures delivered by the prizewinners in the ecomic sciences, together with their biographies, portraits and the presentation speeches at the award ceremonies 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. Below is a list of the prizewinners during the period 1996-2000 with a description of the works for which they won their prizes: J.A. Mirrlees and W. Vickrey (1996) - for their fundamental contributions to the ecomic theory of incentives under asymmetric information; R.C. Merton and M.S. Scholes (1997) - for a new method to determine the value of derivatives; A. Sen (1998) - for his contributions to welfare ecomics; R.A. Mundell (1999) - for his analysis of monetary and fiscal policy under different exchange rate regimes and his analysis of optimum currency areas; J.J. Heckman (2000) - for his development of theory and methods for analyzing selective samples; and D.L. McFadden (2000) - for his development of theory and methods for analyzing discrete choice.