The marine environment is susceptible to a range wide of land-based pollution such as sewage, industrial effluent and terrestrial runoff. Very often the pollution source is either concealed or diffuse without an apparent point of discharge. The tracking of pollution source is essential to accurate assessment of the ecosystem and health consequences as well as effective mitigation and remedial actions. Pollution source tracking is a cross-disciplinary challenge, involving knowledge and skills in microbiology, molecular biology, chemistry, hydrodynamics, etc. This course serves to provide an in-depth understanding of the principle of pollution source tracking, the cutting-edge technology in the field and also case studies from Hong Kong and other parts of the world.