Hairy cell Leukaemia (HCL) has always attracted an interest out of all proportion to its frequency and continues to do so. There are two reasons for this. The first is that the disease is unusually responsive to therapy and second is that it has provided a number of important insights into B-cell biology. This monograph is a comprehensive account of hairy cell leukaemia and aims to provide a more detailed account than is available in the existing literature. The work is timely because a consensus has now emerged concerning accurate differential diagnosis a nd curative treatment. These aspects therefore form the focus of the book and are considered in detail. The basic advances in the laboratory that encourage the belief that elucidation of the underlying oncogenic event in the disease may be within reach. The background to this belief is extensively renewed. As a result the monograph will be of interest and practical value to both clinicians and researchers in this and related fields.