Not only disease patterns but also the contents and concepts of medical services are rapidly changing recent years. A quick look at the evolution of health care services shows that it has evolved in two major ways. First, medical interventions are gradually moving towards the prevention before diseases development. Second, the medical services have become individualized or tailored. The shift to preventive medical care is the most anticipated change in medical services in the 21st century. Theses phenomena are believed as a logical progression in the transition and evolution of medical services, and as a equivalence of the changing medical environment, such as progress in health care technology and changes in life value etc. Clinical practice based on evidence-based medicine is what distinguishes modern medicine from traditional medicine. Preventive medical services have also been established based on scientific evidence. The academic knowledge used as a basis for preventive medical services comes from the investigation of disease etiology, i.e. epidemiology. In the 21st century, the preventive medical service will be differentiated and enlarged to broad areas of medical practice and the target of the service may be focused to the a variety of complex diseases.