How trains behave dynamically as they run along the track - their running behaviour – is a fundamental to railway safety. I am mechanical engineer with 35+ years’ rail industry experience, working in the fields of vehicle design, analysis, and railway safety – both in the UK and overseas. I will endeavour to explain the principles of the individual mechanisms involved, how they work together, and what makes some of them quite unique. I will take time to look at some of the design solutions and approaches used to control dynamic behaviour and some of the risks that are associated. There may also be an opportunity to look at some of the basics behind the maths along the way.