The concept of biomonitoring, the study of biological responses of organisms (both animal and vegetable) to pollutants, is now making rapid strides. The first biomonitoring project was Mussel Watch. During this project, which began in the US around 1965, mussels were systematically collected from approximately 200 sites, their size and weight measured along with the concentration levels of several pollutants. Today, a great number of Mussel Watch projects are up and running in several countries, notably France and the Netherlands where they help provide a scientific overview of marine pollution and track its evolution.