A system of livestock farming in which animals—most commonly, pigs, laying hens, broiler chickens, and veal calves—are kept indoors, with very restricted mobility, for most of their lives. Factory farming has created its own set of environmental damage: raised output of greenhouse gases (farm animals account for 15–20% of methane emissions), and ‘manure surpluses’ (J. Wolch and J. Emel, eds. 1998).