This is a book for medical students and first-year doctors who wish to learn how to approach a patient's symptoms, and sharpen their skills of clinical reasoning and diagnosis. Fifty-four presenting symptoms are discussed, covering approaches and conditions across various medical and surgical disciplines. Each chapter sets out the thought process behind history, examination, and investigations for a symptom, providing a systematic and practical algorithm to distinguish one differential from another. The reader will gain not only a functional approach to patients' presenting complaints, but also learn how to better organize and apply medical knowledge in diagnostic reasoning.