Whales (Cetacea) are divided into two suborders: toothed whales (Odontoceti) and baleen whales (Mysticeti). They are the only mammals that have fully adapted to life in water. There are about 88 recent species, and they inhabit not only the sea but also rivers. They are at the very top of the marine food chain, and the only species that threatens their survival are humans, directly or indirectly, while they have almost no other natural enemies. Whales are among the most endangered groups of mammals. The biggest threats to them are habitat destruction, pollution, global climate change, fishery, accidental catches and noise in the sea. Various international agreements and national laws aim to preserve and protect populations of whales. The science, with its continuous monitoring of whales, adequate research methods and conducting studies on whale-human interactions can contribute to this goal significantly. The consequences of their extinction or a significant decrease in numbers are extremely negative impact on marine ecosystems, and ultimately on humans, due to its role in ocean conservation and climate maintenance.