This volume is a collection of the Nobel Lectures delivered by the prizewinners, together with their biographies and the presentation speeches at the award ceremonies in Stockholm for the period 2001 - 2005. Each Nobel Lecture is based on the work for which the laureate was awarded the prize. This volume of inspiring lectures should be on the bookshelf of every keen student, teacher and professor of physiology/medicine as well as of those in related fields.The following is a list of the Nobel laureates during 2001 - 2005 with a description of the works that won them their prizes:(2001) Leland H Hartwell, Tim Hunt & Sir Paul Nurse — for their discoveries of key regulators of the cell cycle; (2002) Sydney Brenner, H Robert Horvitz & John E Sulston — for their discoveries concerning genetic regulation of organ development and programmed cell death; (2003) Paul C Lauterbur & Sir Peter Mansfield — for their discoveries concerning magnetic resonance imaging; (2004) Richard Axel & Linda B Buck — for their discoveries of odorant receptors and the organization of the olfactory system; (2005) Barry J Marshall & J Robin Warren — for their discovery of the bacterium Helicobacter pylori and its role in gastritis and peptic ulcer disease.