Cancer in children and adolescents is rare and biologically very different from cancer in adults. It accounts for 1·4% of all cancers worldwide, although this proportion ranges from 0·5% in Europe to 4·8% in Africa, largely because of differences in age composition and life expectancy. In high-income countries, survival from childhood cancer has reached 80% through a continuous focus on the integration of clinical research into front-line care for nearly all children affected by malignant disease. However, further improvement must entail new biology-driven approaches, since optimisation of conventional treatments has in many cases reached its limits. In many instances, such approaches can only be achieved through international collaborative research, since rare cancers are being subdivided into increasingly smaller subgroups on the basis of their molecular characteristics. The long-term effect of anticancer treatment on quality of life must also be taken into account because more than one in 1000 adults in high-income countries are thought to be survivors of cancer in childhood or adolescence. The introduction of drugs that are less toxic and more targeted than those currently used necessitates a partnership between clinical and translational researchers, the pharmaceutical industry, drug regulators, and patients and their families. This therapeutic alliance will ensure that efforts are focused on the unmet clinical needs of young people with cancer. Most children with cancer live in low-income and middle-income countries, and these countries account for 94% of all deaths from cancer in people aged 0-14 years. The immediate priority for these children is to improve access to an affordable, best standard of care in each country. Every country should have a national cancer plan that recognises the unique demographic characteristics and care needs of young people with cancer. Centralisation of the complex components of treatment of these rare diseases is essential to improve survival, accelerate research, and train the future specialist workforce. Referral routes and care pathways must take account of the large geographical distances between many patients' homes and treatment centres, and the economic, cultural, and linguistic diversity of the populations served.