In this inaugural lecture, Professor Nigel Wilding explores the computer simulation of changes of state in models for atoms and complex molecules. Predicting the phase behaviour of a material is a central goal of condensed matter science, and a pre-requisite for designing new materials with tailored or novel phase behaviour. Professor Wilding’s lecture outlined how computer simulation of phase behaviour now stands shoulder-to-shoulder with traditional approaches of experimental and analytical theory. He talk focuses on one particularly powerful and flexible computational technique called ‘Monte Carlo simulation’.