In livestock agriculture and the meat industry, a slaughterhouse, also called an abattoir (/ˈæbətwɑːr/ ^ⓘ), is a facility where livestock animals are slaughtered to provide food. Slaughterhouses supply meat, which then becomes the responsibility of a meat-packing facility.

Slaughterhouses that produce meat that is not intended for human consumption are sometimes referred to as knacker's yards or knackeries. This is where animals are slaughtered that are not fit for human consumption or that can no longer work on a farm, such as retired work horses.

Slaughtering animals on a large scale poses significant issues in terms of logistics, animal welfare, and the environment, and the process must meet public health requirements. Due to public aversion in different cultures, determining where to build slaughterhouses is also a matter of some consideration.

Frequently, animal rights groups raise concerns about the methods of transport to and from slaughterhouses, preparation prior to slaughter, animal herding, stunning methods, and the killing itself.

Until modern times, the slaughter of animals generally took place in a haphazard and unregulated manner in diverse places. Early maps of London show numerous stockyards in the periphery of the city, where slaughter occurred in the open air or under cover such as wet markets. A term for such open-air slaughterhouses was shambles, and there are streets named "The Shambles" in some English and Irish towns (e.g., Worcester, York, Bandon) which got their name from having been the site on which butchers killed and prepared animals for consumption. Fishamble Street, Dublin, was formerly a fish-shambles. Sheffield had 183 slaughterhouses in 1910, and it was estimated that there were 20,000 in England and Wales.

The slaughterhouse emerged as a coherent institution in the 19th century. A combination of health and social concerns, exacerbated by the rapid urbanisation experienced during the Industrial Revolution, led social reformers to call for the isolation, sequester and regulation of animal slaughter. As well as the concerns raised regarding hygiene and disease, there were also criticisms of the practice on the grounds that the effect that killing had, both on the butchers and the observers, "educate[d] the men in the practice of violence and cruelty, so that they seem to have no restraint on the use of it." An additional motivation for eliminating private slaughter was to impose a careful system of regulation for the "morally dangerous" task of putting animals to death.

As a result of this tension, meat markets within the city were closed and abattoirs built outside city limits. An early framework for the establishment of public slaughterhouses was put in place in Paris in 1810, under the reign of the Emperor Napoleon. Five areas were set aside on the outskirts of the city and the feudal privileges of the guilds were curtailed.

As the meat requirements of the growing number of residents in London steadily expanded, the meat markets both within the city and beyond attracted increasing levels of public disapproval. Meat had been traded at Smithfield Market as early as the 10th century. By 1726, it was regarded as "without question, the greatest in the world", by Daniel Defoe. By the middle of the 19th century, in the course of a single year 220,000 head of cattle and 1,500,000 sheep would be "violently forced into an area of five acres, in the very heart of London, through its narrowest and most crowded thoroughfares".