There have been a few different ways in use over the years. This page lists them and it seems quite good (just searched Google for your exact question, because I was interested in the answer) http://antoine.frostburg.edu/chem/senese/101/consumer/faq/decaffeinating-coffee.shtml Basically, you can either use solvent extraction (nowadays they do this in such a way that the solvent used is not harmful (water, for example) - in the 70s and 80s, the solvents they chose were quite bad for you, really, and some would inevitably be left behind). These solvents were also bad for the environment. Solvent extraction, if you don't know, is a process used by chemists to get the stuff they want out of a mixture, because the stuff is more soluble in a certain solvent than the rest of the stuff in the mixture. It is a whole interesting area of chemistry by itself, and leads on to all sorts of other fascinating stuff like chromatography. Basically, in layman's terms, they wash the caffeine out of the coffee in a similar way to the way you wash dirt from your clothes. In the not so distant future it may be that genetic engineering is used, because any extraction method is more expensive than if the plant did not contain caffeine in the first place. Hope this helps.

illegally in my opinion!