Edamame are immature soybeans, harvested at about 80% of their growth cycle. They're available both in the pod and shelled, usually frozen, though fresh beans are now showing up in supermarkets. Store fresh edamame in plastic bags in the fridge for up to a week or so. Frozen and well wrapped, the beans will keep for months.
Wash befor cooking using a brush to scrub some of the fuzz off the pods if you like.