This book shows something of the fascination, beauty and power of mathematical ideas. It is based on talks which the author has given to mathematical and scientific audiences, many of whom found the material unfamiliar. The fifteen topics range from the distribution of prime numbers among the integers to the enumeration of the seventeen distinct types of wall-paper pattern. (The standard of mathematics assumed in the reader is roughly that of British university entrance requirements and its equivalent overseas.) The book should be of particular value in sixth-form libraries and to teachers of mathematics at various levels who are looking for new and unusual examples to enliven their work.