This little book discusses a famous problem which helped to define the field now known as topology: what is the minimum number of colours required to print a map so that no two adjoining countries have the same colour, no matter how convoluted their boundaries? Many mathematicians have worked on the problem, but the proof eluded formulation until the 1950s, when it was finally cracked with a brute-force approach using a computer. The book begins by discussing the history of the problem, and then goes into the mathematics on such a level as to allow anyone with an elementary knowledge of...