This book presents readers with the essential aspects of the subspecialty infectious diseases. The second edition of the book includes new developments that are consistent with the published peer-reviewed medical literature and published relevant clinical practice guidelines. The book’s intended audiences are students and medical providers in training. It provides information evolved from prior formal didactic lectures or bedside clinical teaching on clinical infectious diseases, microbiology, and antimicrobial pharmacology that was delivered to help students, residents, fellows, and primary care physicians. Current basic science and clinical concepts regarding each relevant infectious disease topic are still written as a synoptic account to make these topics clear and practical for the readers. The book is organized into 18 parts containing 52 chapters. It adheres wherever possible to a standard pattern of description that aims to define the topic and provide an introduction that would include classification, pathophysiology, and epidemiologic information. The book also lists relevant causative microorganisms; describe the clinical aspects and approach to the topic with the physical examination and relevant laboratory methods, diagnostic imaging, and appropriate antimicrobial therapy. The first part provides introduction to clinical reasoning, antimicrobial stewardship, antimicrobial agents, and medical microbiology. The remaining parts describes the approach to various topics such as: fever of unknown origin, leukocytosis, bloodstream and cardiovascular infections, pulmonary infections, gastrointestinal infections, hepatobiliary infections, hepatic infections, renal–urinary infections, neurological infections, orthopedic-related infections, skin and soft-tissue infections, sexually transmitted infections, infections related to obstetrics and gynecology, eye infections, sepsis, transplant-related infections, ectoparasite-related infections, and infection control and epidemiology. The book’s goal is to help guide the reader through the diagnostic evaluation as well as the process of caring for the patient with an infection.