High Reliability Organisations (HRO) rightly invest significant effort to ensure their Safety Management System (SMS) is effective – for example ensuring appropriate and reliable engineering along with robust and resilient organisational arrangements. The benefits of these arrangements go far beyond mere compliance and contribute to high performance. As well as the organisations themselves, regulators, such as the Office for Nuclear Regulation (ONR), also recognise the importance of these arrangements, actively seeking evidence of their effectiveness within such themes as Leadership, Capable Organisation, Decision-Making and Learning from Experience. Whilst approaches to describing and assessing the visible elements of the SMS can be readily identified, there needs also to be a focus on the cultural and behavioural elements of the organisation’s commitment to safety and high performance. People are part of the system, rather than an unpredictable add-on. An effective SMS will guide and control behaviours with respect to safety. But how do you go beyond the arrangements in order to understand and be confident in the social and interpersonal influences – leadership and commitment, supervision, prioritisation of safety, and so forth? This paper addresses this need to understand and manage the link between the management system and the organisational safety culture, whilst recognising that neither can be considered independently, due to the interconnected nature of complex systems. Considerations are presented to prompt reflections of SMS and organisational culture with respect to compliance and performance.