1. Mutualism: This is when both organisms benefit from the relationship. For example, some types of bacteria live in the guts of animals and help them to digest food, and in return the bacteria receive a safe place to live and a steady food source.

2. Commensalism: This is when one organism benefits from the relationship, while the other is not affected. For example, some types of birds build their nests in trees, which provides them with a safe place to live but does not affect the tree.

3. Parasitism: This is when one organism benefits from the relationship, while the other is harmed. For example, some types of parasites live on or inside other organisms and feed on their tissues.