We know whales, dolphins, and porpoises are the smartest creatures in the sea, we read of their tool use, their self-recognition, their complex songs, and their intricate societies and ability to relate to humans, but, how do we know? And what is the extent of our knowledge of the apparent intelligence of these creatures? Deep Thinkers brings together the top researchers in this field to explain with text and images their findings to all those interested, no prior knowledge required. Deep Thinkers examines cetacean brains, study in the field and in captivity, it compares intelligence markers of cetaceans with birds, bats, and primates, and asks how we define intelligence in non-humans. Deep Thinkers is a truly comprehensive exploration that will set the benchmark for future titles on this topic.