Security is a major concern for protected communication between mobile nodes in a hostile environment. In hostile environments adversaries can bunch active and passive attacks against intercept able routing in embed in routing message and data packets. In this paper, we focus on Black Hole attack in Mobile adhoc networks. MANET has no clear line of defense, so, it is accessible to both legitimate network users and malicious attackers. In the presence of malicious nodes, one of the main challenges in MANET is to design the robust security solution that can protect MANET from various routing attacks. However, these solution are not suitable for MANET resource constraints, i.e., limited bandwidth and battery power, because they introduce heavy traffic load to exchange and verifying keys. MANET can operate in isolation or in coordination with a wired infrastructure, often through a gateway node participating in both networks for traffic relay. This flexibility, along with their self organizing capabilities, are some of MANET's biggest strengths, as well as their biggest security weaknesses. In this paper different routing attacks, such as active(flooding, black hole, spoofing, wormhole) and passive(eavesdropping, traffic monitoring, traffic analysis) are described.