In heraldry, a compartment is a design placed under the shield, usually rocks, a grassy mount, or some sort of other landscape upon which the supporters are depicted as standing (a compartment without supporters is possible but practically unknown, with the exception of South Australia[1]). It is sometimes said to represent the land held by the bearer. As an official part of the blazon it is a comparatively late feature of heraldry, often derived from the need to have different supporters for different families or entities, although sometimes the compartment is treated in the blazon separately from the supporters.

The decorative flourish which was often placed by heraldic artists under the feet, hooves or paws of supporters, chiefly in the 19th century, was disparagingly known by some as the "gas bracket," although this term never had any official currency; the only case in which something similar was ever actually mentioned in the blazon was the "arabesque" vert on which the whale supporters of Zaanstad, Noord Holland, the Netherlands, balance.

Usually when arms are augmented by supporters, a compartment will be added too. In rare cases, a compartment might be granted as an augmentation.

A compartment is usually some kind of landscape (in the case of Scottish chiefs it is generally a "mount vert" [grassy mount] covered with the clan's flower) or seascape, and these can be quite elaborate, particularly in more recent Canadian grants, such as the compartment of the University of Northern British Columbia, in which the female kermodei bear and woodland caribou buck stand on a forest, mountain peaks and ears of wheat, all rising out of the conventionalised heraldic representation of water, which is itself charged with an orca as designed by Ron Sebastian . (Compartments can have a specific piece of geography; Kenya's compartment is Mt. Kilimanjaro.) However, there are some unusual compartments. The arms of the Cumberland County Council has a wall as a compartment, while the Canadian Academy of Engineering has a bridge spanning water. The chief of Clan Donnachaidh has a main in chains as a compartment, while that of Dundas of that Ilk is "a salamander in flames of fire". The arms of Gisborne, New Zealand contain another unique compartment.