For all of human history, we have been eating shellfish (bivalves like clams, mussels, and oysters and crustaceans like shrimp and lobster), and until recently we relied on wild populations of shellfish harvested from coastal areas. However, due to pressure from human harvest and other environmental impacts, the wild shellfish populations are dwindling, particularly wild bivalves. Shellfish producers are increasingly turning to aquaculture, the farming of aquatic organisms, to supply our increasing shellfish demand. In the U.S., the vast majority (by weight) of saltwater aquaculture consists of shellfish, largely clams, oysters, and mussels. The value of shellfish sold in the U.S. in 2013 was over $413 million. Some view shellfish aquaculture as less environmentally damaging, or even environmentally beneficial. However, as shellfish aquaculture becomes increasingly industrialized several concerns have emerged. This fact sheet focuses on the farming of bivalves (clams, oysters, and mussels) in the Pacific Northwest.