Quantifying uncertainty is unavoidable and something that must be done for almost every realistic problem involving decision-making. In particular, quantifying uncertainty for future events or where no data has been observed is becoming increasingly unavoidable and presents many challenges. For over thirty years, researchers from mathematics, philosophy, psychology, statistics, etc., have been working on developing protocols that ensure that expert judgement is treated as scientific data subjected to methodological rules for quality and consistency. This presentation aims to give an overview of the methodological requirements for eliciting structured expert judgements and the different contexts when expert judgement may be necessary. It will also discuss the challenge of validating expert judgements.