The term “liquid crystal” seems like an oxymoron. We are told from an early age that the world can be divided into solids, liquids and gases. In our everyday experience, we encounter crystalline materials such as salt, sugar and gemstones, all of which are very obviously solids. So how can crystals also be liquids? As we’ll see, liquid crystals not only exist, but they are common and extremely useful. We will examine the weird world of liquid crystals, and discuss how they appear in places that range from soap bubbles to mood rings, from video displays to water purification systems.