Dolphins are marine mammals that are closely related to whales and porpoises. They are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture. They are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent dolphins are, as comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition.

Dolphins are social, living in pods (also called "schools") of up to a dozen individuals. They are known to have sex for reasons other than reproduction, sometimes also engaging in acts of a homosexual nature. They are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. They are sound oriented in that they constantly scan their surrounding with bursts of sound. Dolphin echolocation clicks are amongst the loudest sounds made by animals in the sea. They have demonstrated a wide range of sounds and are believed to have a unique 'language' of their own. They are conscious breathers, this means that they have to be awake or semi-conscious to breathe or else they will drown.

Dolphins are mammals, not fish, which means that, like humans, they are warm-blooded, breathe air and give birth to live young whom they feed with milk. Dolphins mate in spring and early summer with the gestation lasting from 10 to 12 months. They are well known for their exceptional learning abilities in captivity, and the songs of whales have been shown to be culturally influenced. They are capable of imitation and memorization; they demonstrate foresight, learn from observation, communicate experience, solve complex problems, perform elaborate tasks, and learn multiple procedures simultaneously.

Dolphins are most often trapped in fishing nets, but everywhere they suffer from some degree of pollution and, conservation experts fear, tourism is also taking its toll on the animal. Dolphins are able to identify each other using their own individual ?signature whistles. Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".

Dolphins gradually build up a network of relationships, ranging from the strong bond between a mother and calf, to casual "friendships" with other community members. They are known to engage in acts of aggression towards each other. These acts of aggression can become so intense that targeted dolphins are known to go into exile, leaving their communities as a result of losing a fight with other dolphins.

They have few animal predators and the biggest threat to their existence is from man. Their brains are about the size of our own. Dolphins have invented a range of feeding strategies that more than match the diversity of habitats in which they live. Dolphins can also use tools to solve problems. They have very sensitive skin, which allows them to detect very small changes in pressure around their bodies. They do not need to drink water as this is obtained from the fish and food that they eat, and they have a sense of taste that they use to tell if a fish is fresh.