Childhood acute leukemias are one of the main causes of death in children aged 1 to 14 years in some countries; and unfortunately, we have been unable to prevent it. Certainly, a good parcel of it is due to the poor understanding about its etiology. This book aims to describe the most important theories and hypothesis regarding childhood acute leukemia. Written by the most outstanding researchers in the field, this book intends to contribute to a greater understanding of the etiology of this disease. It goes beyond the simple and common analysis of risk factors, which hardly allows us to draw definite conclusions. By addressing the etiology of the disease, discussing from molecular biology until epidemiology and clinical manifestations, this book will guide present and future approaches, contributing for a better clinical management of leukemia in children. The knowledge regarding etiology is a crucial step for a better evaluation, prevention and treatment of a disease. Thus, this book finally intends to provide such knowledge, allowing physicians and practitioners to a better manage of childhood acute leukemias.