This report uses new econometric research and a review of previous studies to provide guidelines on the appropriate level and type of demand elasticity to use when analysing a policy proposal. It provides robust elasticity estimates to ensure that policy decisions related to issues such as liberalisation, airport charges, taxation, and emissions schemes, are made on the basis of appropriate and reliable evidence. It provides important new estimates to ensure that price elasticity estimates do not underestimate the sensitivity of passengers to price and are used correctly