Mr Tompkins has become known and loved by many thousands of readers (since his first appearance over fifty years ago) as the bank clerk whose fantastic dreams and adventures lead him into a world inside the atom. George Gamow's classic provides a delightful explanation of the central concepts in modern physics, from atomic structure to relativity, and quantum theory to fusion and fission. Roger Penrose's new foreword introduces Mr Tompkins to a new generation of readers, and reviews his adventures in the light of current developments in physics today.