One of the world's great luxury foods, foie gras (literally, 'fattened liver') is the liver of either duck or goose. Goose, which is considered to be more flavourful and to have the finer texture, is the more expensive. The method used in the production for foie gras from either bird is highly controversial, and involves force feeding them in order that their livers fatten up to the required weight (in the EU, this is 300g - a normal, unfattened liver weighs around 50g).
Banned in the UK, foie gras production is most associated with Gascony, in south west France, but Hungary is also a big producer. Despite the controversy surrounding foie gras, its creamy, silky texture and unique flavour, quite unlike any other liver, means that it remains a sought-after ingredient. It can be bought whole and raw (known as lobes), semi-cooked (micuit) or cooked in paté, block or mousse.
For more information about foie gras regulations see Food Standards Agency.