In this paper I have described mainly the work of our walk-in service for adolescents. I have not described our research into mental breakdown in adolescence which is being carried out through the Centre for the Study of Adolescence. I am aware that I have avoided discussing a number of important issues related to adolescent development and psychopathology, including: the many gaps in our knowledge about adolescence—unknowns which hamper our work severely; the pros and cons of various forms of intervention; the suitability of the various psychopathological categories which are often used to describe what is wrong. Nor have I mentioned our work with parents. Instead I have chosen to describe a few specific areas of our work which are related to assessment and to intervention. By focusing on what I consider to be the main work of the walk-in Centre, I have also tried to describe what we have learned from this kind of work.