An assessment of cooperation and conflict and the role of power in international stability and security from realistic approach is the aim of this article. Realism consists of different branches which despite some hypothetical differences belong to one central core. All realists agree on three main ideas including state-centric approach, the survival principle and self-help. All realistic approaches agree that state is the major player and its aim is to preserve survival in anarchic international environment. The atmosphere of the lack of one single source of sovereignty dictates the self-help rule to the states so that every government could only rely on its own power for its security and survival. Under realistic notions, cooperation in international relations is a variable dependent on power and hardly accessible. The efforts of the states for obtaining relative power and interests are among the factors limiting the possibility of cooperation. The neoliberal approach while accepting some basic notions of realism, emphasizes the absolute interests versus relative interests and looks for ways for cooperation among states. This approach makes the argument that international organizations and regimes are capable of facilitating cooperation and increasing the costs of non-compliance to the mutual obligations.