The term non-Hodgkin lymphoma (NHL) covers a spectrum of malignant disorders arising from cells of the immune system and manifesting predominantly as lymphadenopathy or solid tumour. The classification of NHL is complex and ever-evolving, with more than 50 different subtypes listed in the latest WHO classification of lymphoma (1). In this clinical update, we address the distinction between low-grade (indolent) and high-grade lymphoma, and discuss the principles of diagnosis and management that are of particular relevance to the non-specialist physician who may encounter patients with NHL during their initial presentation, during therapy and during periods of follow-up.