A Mobile Ad hoc Network (MANET) is a collection of wireless mobile nodes that spontaneously form a network without the aid of any established infrastructure. The communication between the nodes is based on multi-hop routing, whereby intermediate nodes relay packets towards their final destination. Ad hoc network inherit the traditional problems of wireless communications, such as interference, bandwidth limitation, limited power, and poor transmission quality, while, in addition, their mobility, multihop nature, and the lack of fixed infrastructure create a number of complexities and constraints that are new to mobile ad hoc networks. Cross layer designs is emerging as new architecture to achieve the arduous communication in MANET. The layered model allows restrictive interaction between the layers. Cross layer designs neglects layered design and allows different layers to inter-communicate the useful information between non-adjacent layers. This book shows that mobile ad hoc network protocol architecture can perform better by exploiting the lower layer information flowing across different layers.