<unk>  is a major field of study within the medical and clinical sciences which focuses on the maintenance, protection, and improvement of the health status of population groups and<unk> es. It is a distinct field of study that may be taught within a separate school of public health or environmental health. The WHO defines<unk>  as:environmental, social, and economic resources to sustain emotional and physical well being among people in ways that advance their aspirations and satisfy their needs in their unique environment.Medical interventions that occur in<unk> es can be classified as three categories: primary care, secondary care, and tertiary care. Each category focuses on a different level and approach towards the<unk>  or population group. In the United States,<unk>  is rooted within primary healthcare achievements. Primary healthcare programs aim to reduce risk factors and increase health promotion and prevention. Secondary healthcare is related to "hospital care" where acute care is administered in a hospital department setting. Tertiary healthcare refers to highly specialized care usually involving disease or disability management. The success of<unk>  programmes relies upon the transfer of information from health professionals to the general public using one-to-one or one to many communication (mass communication). The latest shift is towards health marketing .
Community health
International health
Public health
Drug policy
Organ care system
Outline of public health
Public security
Ethics of organ transplantation