The very first liquid crystalline phases observed were found in derivatives of cholesterol and were accordingly dubbed cholesteric, a term that is used to denote any liquid crystal that exhibits an ordering of molecules similar to these early examples. Cholesteric liquid crystals form in layers that are only a molecule thick, and within each of the layers, the component molecules are ordered with their long axes in the plane of the layer and parallel to each other, analogous to a liquid crystal in a two-dimensional nematic phase. However, unlike nematic liquid crystals, the layers formed during a cholesteric phase are stacked in a rotating, helical manner. In fact, cholesteric phases are only exhibited by chiral compounds.