The rapidly evolving environment of Cyber threats against the NATO Alliance has necessitated a renewed focus on the development of Cyber Defence policy and capabilities. The NATO Modelling and Simulation Group is looking for ways to leverage Modelling and Simulation experience in research, analysis and training to assist the Cyber Defence capability. The remit of NATO Modelling and Simulation Group 117 (MSG-117) ‘Exploiting Modelling and Simulation in support of Cyber Defence’ is to investigate and recommend those aspects of Cyber Defence that could be supported with Modelling and Simulation. To ensure as broad perspective as possible, Task Group members have been drawn from both the modelling and simulation and cyber communities. The Task Group has selected five topic areas for the work: Decision Support System; Cyber Computer Assisted Exercises (CAX) and training programs; Cyber awareness and education; a common set of definitions for Cyber Defence M&S exploitation; M&S environments, synthetic environments, standards, and processes. This paper will focus on the use of Modelling and Simulation in support of decision support, and training and education. First we will address the challenges that M&S faces in supporting these areas. Then we will discuss some promising examples of how M&S can be used in the areas of decision support and in organising and analysing cyber exercises.