Shell middens are refuse deposits composed solely or primarily of molluscan shells. Although they are most frequently thought of as comprising the refuse of ancient human meals, shell waste piles can also be accumulated through other cultural behaviors such as building and industrial activities. The recognition of shell middens in the landscape is not always a simple matter. Some nonhuman animals (e.g., crabs, octopuses, and muskrats) create shell middens. Additionally, a range of natural coastal and landscape processes can generate piles of molluscan shell prompting debates as to their origin.