In simple terms, Health can be defined as free from all diseases and infections. According to the World Health Organization (WHO), Health is not only the absence of disease or illness. It is a state of an active and energetic condition, including physical, mental, and social well-being. A balanced diet and regular exercise play an essential role in maintaining the excellent health of an individual. When the functioning of one or more organs or systems of the body is adversely affected, characterised by various signs and symptoms, we say that we are not healthy, i.e., we have a disease. Diseases can be broadly grouped into infectious and non-infectious. Human Health is a term that can be used to refer to the social, physical and mental well-being of an individual. Its importance and various diseases are discussed briefly in this chapter. Some fatal diseases such as AIDS, cancer and the drug abuse concept are also discussed.