Sickle cell disease was one of the first diseases to be explained at the molecular level. Nevertheless, in the years since the first edition of this book was published, further advances have been made. Much has been learnt about the causes of variability in the natural history of the disease and of the reasons why there are such marked variations in the patterns of morbidity and mortality. The role and importance of genetic modifiers such as alpha-thalassaemia and persisting high levels of fetal haemoglobin, and of the beta-globin haplotype, have been recognized and explored. Studies of the disease which compare geographically separated populations have contributed to understanding this variability. These findings have led to more rigorous thinking about the nature of the disease and a clearer appreciation of how to manage it. This book is intended for professionals: physicians - especially haematologists, medical geneticists, paediatricians, nurses in specialist centres, health planners.