Abstract : This report presents the results of a workshop conducted by the North Atlantic Treaty Organization (NATO) Information Systems Technology (IST) Panel in Istanbul, Turkey, in June 2015 to explore science and technology for characterizing the impact of cyber-attacks on missions. Military mission success is highly dependent on the communications and information systems (CISs) that support the mission and their use in the cyber battlespace. The inexorably growing dependency on computational information processing for weapons, intelligence, communication, and logistics systems continues to increase the vulnerability of missions to various cyber threats. Attacks on CISs or other cyber incidents degrade or disrupt the usage of CISs, and the resulting mission capability, performance, and completion. These incidents are expected to increase in frequency and sophistication. The workshop participants concluded that the key to solving the mission impact assessment problem was in adopting and developing a new model-driven paradigm that creates and validates mechanisms of modeling the mission organization, the mission(s), and the cyber-vulnerable systems that support the mission(s). Such models then simulate or portray the impacts of the cyber-attacks. In addition, such model-based analysis could explore multiple alternative mitigation and work-around strategies an essential part of coping with mission impact and select the optimal course of mitigating actions. Only such a paradigm can be expected to provide meaningful, actionable information about mission impacts that have not been seen before or do not match prior experiences and patterns. The papers presented at this workshop are presented in an accompanying volume, Proceedings of the NATO Workshop IST-128, Assessing Mission Impact of Cyber Attacks.