Abstract: Systems approaches inevitably rely heavily on models to develop understanding and aid communication and decisions. In systems engineering these system considerations and modelling lead directly to a design for a purposeful system or process that is implemented in the real world. In the past systems engineering has been associated with hard, well bounded, precedented problems. This paper considers the changing nature of modern systems and their implications on the practice of systems engineering, with particular focus on the role of models in the engineering of complex systems and capabilities. The paper also discusses the status of systems engineering models at the various stages of the system life cycle, their enduring nature, the fulfilment of stakeholder expectations and the relationship between soft and hard systems methodologies in systems engineering. Finally, the paper highlights the applicability of systems methods that would not be seen as part of a traditional systems engineering approach.