A medical officer of health, also known as a medical health officer, chief health officer, chief public health officer or district medical officer, is the title commonly used for the senior government official of a health department, usually at a municipal, county/district, state/province, or regional level. The post is held by a physician who serves to advise and lead a team of public health professionals such as environmental health officers and public health nurses on matters of public health importance.

The equivalent senior health official at the national level is often referred to as the chief medical officer (CMO), although the title varies across countries, for example known as the surgeon general in the United States and the chief public health officer in Canada.

The national senior adviser on health matters is known as the chief medical officer, while those at state and territory level are mostly known as the chief health officer (CHO), with one CMO and one chief public health officer.

The chief public health officer of Canada is the senior health official for the federal government.

In Ontario, one individual is named chief medical officer of health for the province and has powers to issue guidance, to issue provincial orders, and to coordinate public health responses with medical officers of health, who oversee various public health units.

In British Columbia, the provincial health officer is the senior health official for the provincial government.

The roles of the medical officer of health varies across jurisdictions, but always include responsibilities related to public health and safety, and may include the following functions:

In India, a medical officer generally has a minimum of MBBS degree or MD degree from a recognised medical college and university and his/her name is registered in National Medical Council and in a state medical council. They are posted mainly at primary health centre and community health centres.^{[citation needed]}