An umbrella has a canopy, a main shaft and a plurality of ribs pivotally attached to the main shaft, each rib being of adjustable length and including a pair of outer rib elements, wherein the outer rib elements are flexible and normally adopt a straight configuration aligned with the main shaft in a closed position of the umbrella, and in an open position of the umbrella, flex so that outer ends of the outer rib elements extend generally circumferentially with respect to the canopy. The umbrella can have ribs that would normally be of one piece, in which case accommodation is made for an effective change in the radius of the ribs as the outer rib elements flex. The umbrella may be a folding umbrella with two part ribs. The outer ribs can have a non-uniform cross-section and may taper.