The study of disease and its treatment is a life-long intellectual journey which has engaged some of humankind’s finest minds and kindest hearts. We the authors are still on that fascinating voyage. Every journey begins with a single step and that step is the purpose of this book. It is short enough to be read from cover to cover re-read studied and learnt. This concise and practical introduction to the vast and complex subject of medical treatment is jargon-free and easy to read. It aids in the understanding of everyday situations on the wards in out-patient clinics and in the primary care setting. The handy format is ideal as a ready reference along with its companion volume How Drugs Work Second Edition by Hugh McGavock. It is highly recommended as an undergraduate textbook for students of nursing and medicine especially those embarking on clinical training and is also useful for Nurse Practitioners. Primary care nurses with diagnosis and treatment responsibilities will find the guidance invaluable.