Health care improvement is always on the planning agenda but can prove frustrating when 'the system' seems to have a life of its own and responds in unpredictable ways to reform initiatives. Looking back over 20 years of general practice and primary health care in Australia, there has been plenty of planning and plenty of change, but not always a direct cause and effect relationship between the two. This article explores in detail an alternative view to the current orthodoxy of design, control and predictability in organisational change. The language of complexity is increasingly fashionable in talking about the dynamics oforganisational behaviour and health care improvement, but its popular use often ignores challenging implications. However, when interpreted through human sociology and psychology, a complexity perspective offers a better match with everyday human experience of change. As such, it offers some suggestions for leaders, policy makers and managers in health care: that uncertainty and paradox are inherent in organisational change; that health care reform must pay attention to the constraints and politics of the everyday; and that change in health systems results from the complex processes of relating among those involved and that neither 'the system' nor a few individuals can be accountable for overall performance and outcomes.