Aims : to demonstrate how to perform and interpret sleep studies in both adults and children; to highlight the differences between paediatric and adult polysomnography and polygraphy including the complexities of sleep and respiratory testing along with the limitations, advantages, and pitfalls; to explain how to recognise when different scoring rules should be applied depending on the age of a patient; to explain how to evaluate daytime sleepiness based on self-assessment questionnaires, technical tests and electrophysiological tests.