Depending on the definition of this concept that is adopted, adolescence is the narrow threshold or a vast no-man's land that separates adulthood from childhood. In one -physica1ist- view, adolescence begins when secondary sex characters become noticeable and ends when they are fully developed. In another -socio1ogica1- view, adolescence ends when social independence has been gained. It may easily take many years more to span the interval between those two events. In this collection of papers by specialists from various disciplines, physical, psychological and social aspects of adolescence are considered. The book originates from a postgraduate course for medical practitioners, who deal with adolescents, but the range of the papers is such that we hope it may be of value to a much wider readership, including educators and all who are concerned with adolescents. The course was entitled: 'Adolescence: psychological, social and biological aspects', and was held in Leiden in November 1981. It was the fourth in a series of Boerhaave Courses instigated by the Dutch Growth Foundation of available. which a published record has now become Previous titles are 'Somatic growth of the child' (1966), 'De samenstel1ing van het mense1ijk 1ichaam' (1968) (=Human body composition), and 'Normal and abnormal development of brain and behaviour' (1971). VI The detailed programme of the course was planned by Dr. F.J. Bekker, Prof. Dr. J.L. van den Brande, Prof. Dr. W. Everaerd, Prof. A.Th. Schweizer and Prof. Dr. J.J. van der Werff ten Bosch.