One of the simplest forms of network is to allow each individual to have a set of contacts that it wishes to make (in more formal language each node has a set of half-links), these contacts are then made at random with other individuals based on the number of contacts that they wish to make (half-links are randomly connected) [19] . This obviously creates a network of contacts ( Figure 1 (c)). The advantage of these configuration networks is that because they are formed from many randomly connected individuals, there are no short loops within the network and a range of theoretical results can be proved ranging from conditions for invasion [18, 67, 68] to descriptions of the temporal dynamics [69] . Unfortunately, the elements that make these networks amenable to theoretical analysis-the lack of assortativity, short loops or clusteringare precisely factors that are thought to be important features of real networks.