Lymphomas are solid tumours of the immune system. Hodgkin's lymphoma accounts for about 10% of all lymphomas, and the remaining 90% are referred to as non-Hodgkin lymphoma. Non-Hodgkin lymphomas have a wide range of histological appearances and clinical features at presentation, which can make diagnosis difficult. Lymphomas are not rare, and most physicians, irrespective of their specialty, will probably have come across a patient with lymphoma. Timely diagnosis is important because effective, and often curative, therapies are available for many subtypes. In this Seminar we discuss advances in the understanding of the biology of these malignancies and new, available treatments. Copyright © 2012 Elsevier Ltd. All rights reserved.