Self-harm is a common problem, particularly with the younger population. It is a growing problem with 200,000 presentations to hospital each year in England. It also remains a hidden phenomenon for some young people. Adolescent self-harm is a complex interaction between a variety of factors such as interpersonal, psychological and social factors. The population is extremely heterogeneous and often has coexisting and co-morbid problems. This chapter will discuss the scale of the problem in the UK and globally. It will explore the complexities around its definition and motivations. Some of the risk and protective factors will be explained. The chapter benefits from a case study and description of the promising interventions and treatments. It concludes with what young people have to say about talking to them about their self-harm. The aim is to support professionals involved in supporting young people and their families and carers.