This chapter discusses the principle of cancer immunotherapy in children and adolescents, starting with the most common form of cellular immunotherapy: allogeneic haematopoietic stem-cell transplantation (HSCT). It then discusses specific immunotherapy strategies based on the administration of classic monoclonal antibodies (mAbs) targeting tumour-associated antigens, novel bispecific antibodies that simultaneously target tumour-associated antigens and activate CD3+ T lymphocytes, and mAbs that block key inhibitory molecules of the immune system (checkpoint blockade). Finally, the chapter describes specific cellular immunotherapy approaches, such as tumour vaccine and adoptive transfer of immune cells. Although only a few immunotherapies have so far been incorporated into the standard practice for paediatric cancers, their role is enjoying a new revival, after the promising results obtained in recent clinical trials.