The Pacific geoduck, scientific name Panopea generosa, is a species of very large, edible saltwater clam in the family Hiatellidae. The common name is derived from a Lushootseed (Nisqually) word gʷídəq.

The geoduck is native to the west coast of North America. The shell of the clam ranges from 15 centimetres (5.9 in) to over 20 centimetres (7.9 in) in length, but the extremely long siphons make the clam itself much longer than this: the "neck" or siphons alone can be 1 metre (3.3 ft) in length. The geoduck is the largest burrowing clam in the world. It is also one of the longest-living animals of any type, with a lifespan of up to 140 years; the oldest has been recorded at 168 years old.

The large, meaty siphon is prized for its savory flavor and crunchy texture. Geoduck is regarded by some as an aphrodisiac because of its phallic shape. It is very popular in China, where it is considered a delicacy, mostly eaten cooked in a fondue-style Chinese hot pot. In Korean cuisine, geoducks are eaten raw with spicy chili sauce, sautéed, or in soups and stews. In Japan, geoduck is prepared as raw sashimi, dipped in soy sauce and wasabi. On Japanese menus in cheaper sushi restaurants, geoduck is sometimes substituted for Tresus keenae, a species of horse clam, and labeled mirugai or mirukuigai. It is considered to have a texture similar to an ark shell (known in Japanese as akagai). Mirugai is sometimes translated into English as "giant clam", and it is distinguished from himejako sushi, which is made from Tridacna gigas.