The need for modernisation of simulation capability by the United Kingdom Ministry of Defence (UK MOD) is being driven by a number of factors, including the need to: Provide a more agile and cost effective approach for rapidly delivering simulation capability to meet the increased and diverse use of simulation across MOD; Capitalise on the benefits of technological developments in the IT industry and align with UK MOD ICT (Information & Communication Technology) and NATO strategies e.g. ‘cloud first'; Promote the re-use of simulation resources across the UK Defence Enterprise to reduce acquisition of simulation capability and reduce the through-life costs. The UK MOD is researching the provision of Modelling and Simulation as a Service (MSaaS) as a potential Enterprise-level strategy to meet these needs and provide recommendations to de-risk the approach. This paper provides an overview of the UK MOD's research's into implementing an MSaaS capability. It describes the elements of the MSaaS ecosystem and the stakeholders that interact with it. The paper highlights the challenges an Enterprise will face that wants to implement an MSaaS capability and describes issues that need to be resolved if the Enterprise wants to share its simulation resources with other organisations. Use cases are described to demonstrate how MSaaS can support the needs and provide benefits to different operational users. These include training, mission rehearsal, concept development and experimentation (CD&E), crisis management and data farming. Recommendations are made for a phased approach for delivering an MSaaS capability and the paper identifies where further research is required.