Lifetime prevalence of self-harm (self-poisoning or self-injury) is 5–6% in the UK adult population. Rates are increasing especially among young women, where lifetime prevalence is now 25%. The commonest immediate causes are social and interpersonal problems. The most commonly associated mental health problems are mood disorders and alcohol misuse. Assessment involves careful characterisation of the act of self-harm, the person who self-harms and their social circumstances, but should not entirely be focussed on risk. It should identify needs in mental health or physical health, social needs and psychological needs, and should be a therapeutic experience for the person who has self-harmed. The assessment itself may be helpful for some. Research into cost-effective treatment is limited, but even so it is reasonable to offer brief psychological therapies to everybody and longer-term therapies to those with severe repeated self-harm. Quality improvement activities should aim to improve the experience for people making contact with mental health and to increase the availability and accessibility of therapeutic interventions for self-harm.