This training day, organised by YHEC, aims to provide the participant with a sufficient grounding to effectively critique and validate models. The training day will be particularly useful to those people who commission health economic models, or use models to help make decisions. As well as discussing the strengths and uses of economic modelling, the training day will also explore the limitations and constraints of different approaches and will explore a number of commonly-observed errors in models. Please note that this training day has not been designed to teach delegates how to build models; instead, the course is aimed at those who will review or depend on models built by other researchers.