Models for understanding young people and their development are fundamental prerequisites in planning programs to help and control young delinquents. Evidence indicates that community alternatives to custody do not in themselves offer better results for young people or for society. Equally, it can be shown that by building on defensible and testable developmental and environmental models, programs can be created both within and outside physical institutions to protect young people from further harm and allow many to mature and even avoid reoffending. A decline in the extent of juvenile imprisonment in Spain is reported. 32 references