This chapter addresses how to make the six-party talks a success in not only resolving North Korea's nuclear issue but also promoting security cooperation among six countries in Northeast Asia. It also addresses how to reduce military tension and build a durable peace on the Korean Peninsula. The chapter explores ways to promote multilateral security cooperation in Northeast Asia after having resolved the North Korea's nuclear issue and reduced tension on the Korean peninsula in the future. It discusses United States, China, Japan and Russia's strategies and policies toward North Korea. South Korea's policy toward North Korea faced grave challenges after North Korea's missile test launches and nuclear test. It is critical that Northeast Asian countries collectively resolve the North Korean nuclear issue before entering any serious discussion about the multilateral security cooperation. There are limitations in functionalist and neofunctionalist approaches to regional cooperation in Northeast Asia, mainly through economic exchanges and cooperation.