This book introduces the up-to-date knowledge of managing FUO (fevers of unknown origin), discusses the etiology and distribution of disorders causing FUO, helps clinicians in differential diagnosis of the wide range of disorders which have the clinical manifestation of fever. The diagnosis and treatment of FUO is one of the most challenging topics recognized in clinical practice. Detailed history, physical examination, and laboratory tests in the differential diagnosis of the FUO patient are also of key importance. This book contains experiences in the diagnostic approaches of FUO and summarizes the clinical practice routine for these patients. The major parts of this book include cases of infectious diseases, non-infectious inflammatory diseases, malignant disease and others. A full view of differential diagnoses and clinical management are presented to help the readers know how to manage the patients when facing similar cases in clinical practice. Concise literature review, including guidelines is also provided for a better understanding of the disease diagnosis and treatment. More general principles of empirical therapy and a handful of specific indications are further demonstrated.