Advances in wireless communications and networking technologies are rapidly making the anywhere anytime wireless access a reality. Wireless ad hoc networks (WANETs) have been largely deployed due to its several promising benefits over the wired networks. The deployment of WANET is in various forms which include mobile ad hoc network (MANET), vehicular ad hoc network (VANET), opportunistic network or delay tolerant network (DTN), and mobile social networks. Disaster recovery communications, military/tactical communications, mobile social networks, vehicle-to-any (V2X) communications, mobile sensor networks are some major applications of WANET which have been widely deployed today. Data delivery in WANET, especially in mobile and hostile environments, poses great challenges due to the infrastructure-less environment, mobility, unreliable wireless link nature, effect of terrain, and distributed nature of wireless devices. In this thesis, we propose data delivery solutions for challenging wireless networks with major focus on opportunistic networks. We exploit adaptive data forwarding strategies, cooperation opportunities, openair wireless medium nature, communities and ties in social network nature, and multiple network interfaces to tackle such challenges and improve the system performance. Firstly, we study the mobility models in WANET. The synthetic mobility models are widely used in the WANET research for network simulations and performance evaluations. Group mobility model is of particular interest as group motion occurs commonly in scenarios where WANETs are deployed, such as disaster recovery operations, military operations, and mobile social Author's Publications References List of Figures 2.1 Classification of group mobility models. References to these