Radicchio is member of the chicory family along with endive and escarole. It grows in a tight head, like cabbage.
Radicchio is most commonly used in fresh salads for it’s pungent, peppery flavor, though it can also be sautéed or grilled. Cooking will mellow the sharp flavor.
Store radicchio as you would other greens like cabbage or lettuce, unwashed in a plastic bag in the fridge.