Much of early medicine was practiced by trial and error, but ancient peoples also looked for causes and cures for disease by studying the body and observing the sick. In Greece during the 5th century bc, the physician Hippocrates stressed that medical care was a science that could be learned through clinical observation and experimentation. The connection between health and hygiene was made in several ancient cultures, including those of India and Rome. The Romans drained marshes where malaria-carrying mosquitoes bred, and they built underground sewers and aqueducts to carry clean water in the cities. Laws governed the cleanliness of streets and the storage of food.

Because of limited contact between cultures, most early knowledge of the efficacy of various measures did not spread from place to place. With the collapse of the Roman Empire around ad 400, much medical knowledge was lost, to be replaced by superstition. It was not until the 14th century that a medical renaissance began. Thereafter, progress occurred exponentially. Accurate descriptions of the structure and functioning of the human body were made, and the invention of the printing press in the middle of the 15th century enabled this information to be published and easily disseminated. The development of microscopes in the late 16th century prompted the discovery of microorganisms, although it was not until the 19th century that scientists were able to show that bacteria and other microbes caused disease. Also in the 19th century, people recognized the importance of sanitation and cleanliness, improving the survival rate in hospitals. Anesthesia was discovered and the first vaccines were produced.

During the 20th century, the importance of vitamins and other nutrients in preventing disease was recognized. Antibiotics, sulfa drugs, blood types, and genes that cause disease were discovered. A host of diagnostic and surgical tools were created that incorporated inventions such as X rays, fiber optics, lasers, and computers. Techniques such as organ transplantation (Medical Transplantation), kidney dialysis, dental implants, gene therapy, and fetal surgeries were introduced. Thousands of new drugs were developed to treat everything from ulcers to zinc malabsorption.

The list of medical techniques for fighting disease continues to grow. More effective methods are expected to be introduced in the coming years as scientists gain a better understanding of such subjects as the molecular biology of normal and abnormal cells, gene structure and action, and the relationship between environmental stresses and disease.