Mutualism is an interaction that confers benefits to both the interacting species.
Examples:

• Mycorrhizae represent a close mutual association between fungi and the roots of higher plants. Fungi help the plants in absorption of nutrients, specially phosphorus, while the plants provide food for the fungus.
• Lichens represent an intimate mutualistic relationship between a fungus and photosynthesing algae or cyanobacteria. Here, the fungus helps in the absorption of nutrients and provide protection, while algae prepare the food.