Mussels are one huge extended family. They're black bivalve mollusks (with two hinged shells) with an orange to yellowy brown flesh. You can get wild or cultivated mussels, often attached to rocks in bunches or on thick wooden piles attached to the seabed. Be aware that they are often found in polluted areas, where they are used to clean the water.
They can be eaten all year round, fresh, frozen or tinned.
When choosing mussels: if they're fresh, make sure they're properly closed, shiny and heavy. If buying fresh, make sure they are fit for consumption.
There are over 70 types of mussels. They're found in large quantities in cold waters like the Channel and the Atlantic, as well as in Spain and the Med, where they tend to be a lot larger.
Mussels grown on piles at sea (also called bouchots) are renowned for their taste.
Larger mussels from Spain or the Mediterranean have whitish flesh and sometimes less flavor, but are more practical for frying or skewering, and can also be eaten raw.