As the linchpin of future stability in Northeast Asia and dictator of the security posture of the peninsula, the actions of North Korea (DPRK) have immense implications for China’s national security and the broader security environment in the region. Beyond the two states on either side of the 38th parallel, China is the most important stakeholder in the final outcome of issues on the Korean peninsula, and thus will continue to be an indispensable actor in any future solution to denuclearization and unification. China’s willingness to play a positive role in finding a solution amenable to all parties will, in large part, depend on Beijing’s cost-benefit analysis of North Korea’s value to China, which, in turn, ultimately rests on the Chinese leadership’s assessment of the security implications of North Korea’s behavior for China. These implications can be divided into direct and indirect, as well as both positive and negative aspects, for China’s leaders to factor into their decision-making process. This chapter will address the security side of the Sino-North Korean relationship by focusing on the rationale behind China’s policy; the growing domestic debate over that policy; the evolving security implications of the policy; and how these changes may affect China’s policy going forward.