Intellectual connections such as these are why so many physicists are interested in problems in finance and, in part, why so many have been recruited into the financial sector. It also helps that physicists tend to be good at computer modelling and working with large data sets. The March 2013 edition of Nature Physics was devoted to the latest academic research into the links between physics and finance. Much of this is in the emerging area of “complex networks”, which aims to describe the behaviour of systems containing a number of interconnected discrete elements. Complex networks are known to have a very wide range of applicability: a biological cell can be viewed as a network of chemicals linked through chemical reactions; the world wide web is a network of webpages connected by hyperlinks; and food webs are used by ecologists to model the relationships between different species.