Human beings are highly complex and complicated systems, with many interacting processes from the chemical to the mechanical, and from the molecular to the musculoskeletal. If we want to "look inside" these incredible machines we cannot simply dismantle them. Some parts of the system can be directly measured, but most parts are hidden. Systems modelling provides a means of inferring what is hidden and making knowable what was previously unknown. However, sometimes these inferences are misleading and the unknown is actually unknowable. We'll touch on understanding movement from motion capture and aspects of systems pharmacology - the study of drug action from a systems perspective.