Depends on how dull ya let it get before it gets sharpened. If I get a knife and the egde is practically rounded, I'll use a medium diamond impregnated sharpening pad to define the edge, a fine Arkansas oil stone to do the actual sharpening and an extra fine Arkansas oil stone to polish and refine the edge.
After I'm happy with it, I'll use an extra fine diamond impregnated sharpening rod every now and then to keep it sharp.