Mammals populate all land and marine habitats. The first true mammals evolved 220 million years ago. To date, they retained their basic physical characteristics of the species. Marine mammals are animals that made most progress of all land vertebrates in terms of adaptation to life in the water. The adaptation was brought about by an abundance of food from the sea and by seeking a refuge from land-based predators. The relationship between humans and marine mammals evolved from an intensive exploitation and destruction to up-todate efforts to save certain marine mammal species from extinction. At present, new initiatives brought forward by scientists and experts as well as the efforts in making society more aware of the fact that a preserved environment and the nature are the most important resources - in terms of the economic development of the country - do not give the expected results in preserving the environment. Due to its geographical location and the diversity of the local terrain, Croatia exhibits - considering its size - a very large number of diverse types of habitats as well as a large-scale biodiversity. The Adriatic Sea Area is particularly important in terms of this large-scale biodiversity. Within a marine ecosystem, the most endangered species are those found at the top of the food chain, where marine mammals are found as well.