What are the risks? How big are they? ‘Resilience’ considers some central questions faced by structural engineers. Structures are safety critical—when they fail people may be killed—but no human activity is risk free, so how safe is safe enough? Scientific knowledge is necessary but not sufficient. Many assessments and assumptions have to be made about what may happen in the future. Risks can be predicted and controlled, but by their very nature the answers are partial because of system and human uncertainties. Systems-thinking provides a common language for hard and soft systems and examines how the most promising way of re-integrating those professions fragmented by specialisms.