Mammals come in a bewildering variety of shapes and sizes and yet all of the 4700 or so species have some characteristics in common, which justifies the inclusion of diverse types within a single group. Although mammals evolved on land, a number of species have become adapted to spending part or all of their lives in water and it is these mammals that you are going to concentrate on in this course. You will meet some aquatic mammals, find out how we can study them, consider their evolutionary history and read about human impacts on one iconic group.