Written by the 1960 Nobel Prize winner in the field of immunology, this volume explores the nature and limitations of scientific pursuit. The three essays touch on some of mankind's greatest questions: Can science determine the existence of God? Is there one scientific method by which all the secrets of the universe can be discovered? The book aims to define the limits of science. The author's central purpose is to exculpate science from the reproach that it is quite unable to answer those ultimate questions that he shows to be beyond its explanatory competence. This charge, he argues, is no more sensible than to reproach a railway locomotive for not flying. But in spite of this he believes science to be a great and glorious enterprise - the most successful that human beings have ever engaged in. Peter Medawar is the author of Advice to a Young Scientist, Pluto's Republic, Memoir of a Thinking Radish and Aristotle to Zoos (with Jean Medawar).