This paper from the State Department's Bureau of International Security and Nonproliferation outlines the challenges of noncompliance. The costs of noncompliance include undermining the assurance against proliferation, the foundation of trust and safety, efforts to bring about universal adherence to the Nuclear Nonproliferation Treaty (NPT), and the aspirations for general and nuclear disarmament. The paper also reviews the obligations of NPT states under Articles I, II, and III of the NPT. The paper concludes by looking at the cases of Iran and North Korea, and reinforcing the need to develop and implement ways to deter, detect, and reverse noncompliance.
U.S. Department of State: http://www.state.gov