An arsenal is a place where arms and ammunition are made, maintained and repaired, stored, or issued, in any combination, whether privately or publicly owned. Arsenal and armoury or armory are mostly regarded as synonyms, although subtle differences in usage exist.

The Watertown Arsenal was a major American arsenal located on the northern shore of the Charles River in Watertown, Massachusetts. The site is now registered on the ASCE's List of Historic Civil Engineering Landmarks and on the US National Register of Historic Places, and it is home to a park, restaurants, mixed use office space, and formerly served as the national headquarters for athenahealth.