Absinthe is a bitter green liquor containing large amounts of anise and wormwood (artemesia absentium), no longer legally available in most countries. It's very high alcohol content belies it's primary power— the psychotropic toxin thujone, which is derived from the wormwood.

Absinthe is imbibed only in dilute 50% sugarwater mixtures because of it's harsh taste, but is appreciated because it has long been believed that it's particular high promotes artistic creativity. Lovers of absinthe dubbed it "the green fairy", whereas opponents of it dubbed it "the green devil". The gothic and romantic literary movements were closely associated with absinthe.

The liquor first distilled in 1792 by Dr. Pierre Ordinaire, a Frenchman living in Switzerland, was designed to be a medicinal tonic. Through all the sugar you can dissolve, cutting past licorice and alhcohol and herbs is an amazing bitterness. It is the black bitter licorice you can never find, distilled to a pure essence.

A whole culture sprang up around absinthe when it was the rage, but the (false) reputation that it induced madness and sterility caused it to be banned in most countries. Popular absinthe makers dropped the wormwood and upped the anise content, resulting in the modern day liquors of Pernod, Ricard and Herbsaint. Today, though legal enforcement is relatively lax, it is illegal to sell absinthe. However, all of it's ingredients (including wormwood) are legal to sell, and so several recipes exist on the web.

The Absinthe FAQ page contains recipes for concocting absinthe.