Objects that differ from their mirror images, such as the left and right hands, play an important role in physics at all lengths scales, from elementary particles to macroscopic systems. The handedness, or chirality, of molecules in liquid crystals has a remarkable influence on the macroscopic physical properties of these systems, including the appearance of new phases. Indeed, the majority of optical applications of liquid crystals is due to chiral structures, namely the thermochromic effect of cholesteric liquid crystals, the optical activity in twisted nematic liquid crystal displays, and the ferroelectric and antiferroelectric switching of smectic liquid crystals.