Nodes in the MSN communicate with each other in a store-carry-and-forward mode with the short range communication techniques. Only when two nodes come within the transmission range, there is an opportunistic link between them to exchange information. Therefore, the mobility patterns of nodes have a significantly influence on the information dissemination in MSNs. Recently, some complicated models have been employed to predict the mobility patterns of nodes, such as Edge-Markov model [38]. However, due to the complexity, it is still difficult to use the above algorithms in practice. Thus, some simple mobility models are still required, such as [39, 40], although the performance cannot be completely guaranteed. Most of these models indicate that the inter-contact time between two nodes conforms to an exponential distribution [41]. Karagianis et al. [42] also shows that an exponential decay of inter-contact time between mobile devices is reasonable. Therefore, we assume that the inter-contact time between two nodes follows an exponential distribution with parameter X in this chapter. The probability that two nodes encounter with each other within [t, t + At] becomes