Lymphomas are especially dangerous due to the interconnection of all the lymph nodes in the body. A range of pathological techniques have evolved to aid the understanding and diagnosis of malignant disease. Three factors are especially significant in assessing a tumour: its size, its rate of growth, and the rate of multiplication of its cells. Using calculations based on these factors, it is now possible to make far more accurate predictions about the future growth and the course of the disease than have been previously possible, with the result that therapy can be much more precisely tailored. This book reviews the methods used to assess cell proliferation specifically in lymphomas, with brief details of technique where appropriate, and examines their implications for diagnosis and treatment.