Radicchio (Italian Chicory) is a leafy vegetable with white-veined red leaves. It is often confused with the purple cabbage but it actually belongs to Asteraceae, the lettuce, artichoke and sunflower family (Cabbage belongs to Brassicaceae).
Radicchio have a bittersweet, spicy taste which is supposed to mellow when is grilled or roasted. It has been used in foods since ancient times - Pliny, the Elder wrote of it in Naturalis Historia, and harped about its medicinal properties claiming that it was useful as a blood purifier and as a sleep aid. In fact, radicchio does contains intybin, which is a sedative/analgesic so Pliny had it right all those centuries ago.
Radicchio also contain very high levels of anthocyanins (duh! They're purple!). Most often, radicchio are used in fresh salads with lettuce and other spring greens.