Biomembranes are unique states of soft matter that share some of their materials properties with the mesophases of liquid crystals. Although of genuinely fluid character, membranes can display ordered states under physiological conditions, and it appears that their lateral organization and the related functional properties are intimately coupled to states in-between order and disorder. Hence, the liquid-ordered state of membranes, which owes its existence to the unique ability of cholesterol to mediate between order and disorder, has moved center stage in the characterization of membranes in terms of domains or rafts.