This is an incomplete list of notable mutualistic symbiotic relationships, in which different species have a cooperative or mutually dependent relationship.

• Algae with fungi in lichens
• Anglerfish with the bioluminescent bacteria that illuminate its 'lure'
• Ants with aphids and with some caterpillars
• Cleaner fish or Cleaner Shrimps with other large fish like groupers, sharks and moray eels
• Corals with zooxanthella
• Flowers with pollinators such as bees
• Goby fish with a shrimp
• Humans with cultivated plants and with domesticated animals
• Leafcutter ants with the fungus they 'farm'
• Legumes with Rhizobia (nitrogen-fixing bacteria)
• Deep-sea pompeii worm and the thermophilic bacteria which grow on it
• Ratel or 'honey badger' with the honeyguide bird
• Ruminants such as cows and their intestinal bacteria which break down cellulose
• Sea anemones with clownfish, crabs or shrimps
• Termites with their intestinal bacteria which digest cellulose
• Mitochondria with eukaryote cells