Book excerpt: What variables are relevant to predict the future results of a football team? Are there any inefficiencies in the betting markets that can be exploited? How many games are necessary to correctly measure the level of a team or a footballer? Is it better to bet on a team that is on a winning streak or is it better to bet on a team that is on a losing streak? What is the probability that a team that has just been promoted will be relegated in the next few seasons? What is the optimal size and composition of a team squad? How are the best and worst clubs different? What are the best bookmakers? In this book the reader will find the answer to these and many other questions about the beautiful game, thanks to data mining techniques applied to a historical database of more than 200,000 football matches and a statistical approach explained in an easily accesible style.