This chapter vividly details Communicable diseases and Non Communicable diseases of Public Health Importance. Viral diseases like chickenpox, Measles, Mumps, Influenza, Polio, Rabies, Dengue and SARS are described. Bacterial diseases like Diphtheria, Whooping cough, ARI, Meningitis, TB, Cholera, Diarrhoea, Anthrax, Plague, Leprosy and Typhoid are described. Parasitic diseases like Guinea worm, Scabies, Malaria are given priority. Non-communicable diseases like Diarrhoea, Hypertension, Cancer and CHD are briefly outlined. Ongoing major National Health Programmes are detailed to include the duties of Health Inspectors of a PHC. STD and RCH are given emphasis in their public health approach. National Family Welfare Programme is highlighted along with its objectives.