Understanding Medical Education is a series of occasional papers designed to meet the needs of all newcomers to medical education,whether undergraduate or postgraduate,including those studying at certificate,diploma and master level. Understanding Medical Education aims to provide an authoritative,up-to-date and comprehensive resource summarising the theoretical academic bases for modern medical education practice. This paper describes the key concepts fundamental to good assessment reliability,validity,educational impact,cost-effectiveness and acceptability. No single assessment instrument is perfect and a good assessment programme will encompass a variety of test methods. The authors summarise the strengths and weakness if the most popular assessment methods in medical education today and discuss how the s if these may be combines and standards set. This is an essential introduction to assessment for all medical educators by two of the foremost academics in the field.