Once upon a time – thirty long years ago, even? – icons were images to be worshipped. Today ‘iconic’ is an overused word for the paradigmatically famous. Not just famous, but so famous as to cause intense feelings of love and, more rarely, hate. Prince Charles’s first wife was pretty well-known anyway, but she became an icon. It’s not clear why, but she did. His second wife is merely famous and definitely not an icon. You need something extra to become iconic. Being beautiful helps, but it is not mandatory. Mao was an icon but he wasn’t pretty. Dying young in a car crash (Diana, James Dean), being assassinated (Kennedy, Che Guevara), committing suicide (Marilyn), or being crucified (Jesus) is a major step forward in one’s career towards icondom. But only a step: a complex historical and cultural process is required to transform an image into an icon. Martin Kemp picks a number of ‘icons’ and writes erudite essays about each: Jesus Christ, the Cross, the Heart (as in I ♥ NY), the Lion, the Mona Lisa, Che, the US flag, the photograph of the napalmed Vietnamese girl running naked, the classic bottle of Coca-Cola, the double helix of DNA, and E=mc2.