Is there a 'physics of society'? Ranging from Hobbes and Adam Smith to modern work on traffic flow and market trading, and across economics, sociology and psychology, Philip Ball shows how much we can understand of human behaviour when we cease to try to predict and analyse the behaviour of individuals and look to the impact of hundreds, thousands or millions of individual human decisions, whether in circumstances in which human beings co-operate or conflict, when their aggregate behaviour is constructive and when it is destructive. By perhaps Britain's leading young science writer, this is a deeply thought-provoking book, causing us to examine our own behaviour, whether in buying the new "Harry Potter" book, voting for a particular party or responding to the lures of advertisers.