The effects of magnetism have been known since antiquity. For example, a piece of the naturally occurring iron-oxide mineral known as lodestone can behave just like a manufactured magnet. Today, magnets play an increasingly important role in our everyday lives. Electric generators, simple electric motors, television sets, cathode-ray displays, tape recorders, and computer hard drives all depend on the magnetic effects of electric currents. This unit explores the properties of magnets and the magnetic fields they produce. It also reveals the fascinating, and unexpected, connection between magnetic fields and electric currents.