Abstract: Wireless network consist of wireless node without any administration. Due to present of mobility of nodes, the network is easily personated by several attacks. In 1980’s Mobile ad hoc network s have been widely researched ` for many years. Ad hoc network is a collection of nodes that is connected through a wireless medium forming rapidly changing topologies .The infrastructure less and dynamic nature of these network demands new set of networking strategies to be implemented in order to provide efficient end to end communication. Wireless devices are constantly grooving in communication field having more computing speed and a number of features, while shrinking in weight and size. The ad hoc network is made up of multiple nodes connected by links since link can be connected as well as disconnected at any time. The ad hoc network inherits the some traditional problem of mobile communication as well as wireless. Routing in mobile ad hoc networks in challenges task due to its frequent changes in topology. We discuss in this paper routing protocol, challenges and security of ad hoc network