A quantitative limit placed on the importation of specific commodities. The protection afforded by quotas is more certain than can be obtained by imposing import duties as the effect of the latter will depend on the price elasticities of the imported commodities. Quotas, like tariffs, can also be used to favor preferred sources of foreign supply. Quotas may be specified as an absolute limit or changed from year to year in response to changes in domestic supply and demand.