This book is a companion to the WHO manual entitled "Management of the Child with a Serious Infection or Severe Malnutrition: Guidelines for Care at the First-Referral Level in Developing Countries." It is aimed at medical, nursing and other healthcare students, and presents a summary of the technical background and the evidence-base underlying the clinical guidelines. For treatment recommendations, the companion manual should be consulted. The book focuses on the major causes of childhood mortality dealing with disease definition, burden of disease, etiology, pathophysiology, clinical features, and management. It will be a useful companion study guide to complement undergraduate education in pediatrics in medical and nursing schools.