The National Aquarium – also known as National Aquarium in Baltimore and formerly known as Baltimore Aquarium – is a non-profit public aquarium located at 501 East Pratt Street on Pier 3 in the Inner Harbor area of downtown Baltimore, Maryland in the United States. Constructed during a period of urban renewal in Baltimore, the aquarium opened on August 8, 1981. The aquarium has an annual attendance of 1.5 million visitors and is the largest tourism attraction in the State of Maryland. The aquarium holds more than 2,200,000 US gallons (8,300,000 L) of water, and has more than 17,000 specimens representing over 750 species. The National Aquarium's mission is to inspire conservation of the world's aquatic treasures. The aquarium's stated vision is to confront pressing issues facing global aquatic habitats through pioneering science, conservation, and educational programming.

A public aquarium (pl. aquaria) or public water zoo is the aquatic counterpart of a zoo, which houses living aquatic animal and plant specimens for public viewing. Most public aquariums feature tanks larger than those kept by home aquarists, as well as smaller tanks.