The World Health Organization (WHO) Classification of Tumours provides a definitive classification of all tumours, worldwide. This is essential to underpin the diagnosis and treatment of cancer, as well as research and education. Without it, clinical trial results could not be compared between countries, research results could not be evaluated collectively and epidemiological studies based on cancer registration would be impossible. The classification will help move the field forward by being based on a forwardlooking multidisciplinary effort grounded in genetic advances, with an eye on worldwide applicability. An overview of the classification and its salient features are provided in two typescripts, which cover the classification of myeloid and histiocytic/dendritic neoplasms and the classification of lymphoid neoplasms. Added to this is the recent 'HUGO Gene Nomenclature Committee (HGNC) recommendations for the designation of gene fusions'. In this typescript a group of experts under auspices of the Human Genome Organization’s (HUGO) Gene Nomenclature Committee (HGNC) proposes using double colons (::) as the official designation for fusion genes. The Leukemia Editors strongly support the HGNC recommendation and request authors use the HGNC nomenclature in submissions to Leukemia and other journals. The goal of HUGO and HGNC is to provide unique symbols and names for human gene loci including protein coding genes, non-coding RNA genes and pseudogenes with the purpose of unambiguous scientific communication.