This chapter presents the current state of the art of mobile ad hoc network and some important problems and challenges related to routing, power management, location management, security as well as multimedia over ad hoc networks. A mobile ad hoc network (MANET) is a temporary, self-organizing network of wireless mobile nodes without the support of any existing infrastructure that may be readily available on the conventional networks. Since there is no fixed infrastructure available for MANET with nodes being mobile, routing becomes a very important issue. In addition, we also explain the various emerging applications and future trends of MANET.