Confusingly, three different, unrelated plants are all known by this name.
The globe artichoke is related to the thistle. Its leaves are edible, as is the bottom part of the flower, called the heart (which you can also buy tinned or frozen). Globe artichokes make a delicious starter simply boiled whole and served with melted butter, mayonnaise, hollandaise or vinaigrette for dipping the leaves. Break off each leaf and draw the soft fleshy base through your teeth. Once you've removed all the leaves, you can pull or slice off the hairy 'choke' and then eat the heart and the meaty bottom with the remaining sauce.
The Jerusalem artichoke belongs to the sunflower family and it's the plant's underground tubers that are eaten. They're rather knobbly and irregular in shape, with a pale brown or purple-red skin. Scrub them and boil or steam until tender and then peel. If a recipe calls for peeled Jerusalem artichokes, peel them and drop into acidulated water until ready to use to stop them from discolouring.
The Chinese artichoke is a perennial herb of the mint family, grown for its edible tuberous underground stems. It has a sweet, nutty taste, similar to the Jerusalem artichoke. It's much more difficult to find in shops than globe or Jerusalem artichokes.