The three types of symbiotic relationships are commensalism, mutualism, and parasitism.
Commensalism: One organism benefits from the symbiotic relationship while the other remains unaffected. Example: Barnacles and whales.
Mutualism: Both organisms benefit in the symbiotic relationship. Example: Humans and the bacteria in their digestive tract.
Parasitism: One organism in the symbiotic relationship benefits at the other organism's expense. Example: Fleas and dogs.