In recent years the Rogowski-coil method of measuring electric current has developed from a ‘laboratory curiosity’ to a versatile measuring system with many applications throughout industry and in research. The technique possesses many features which offer an advantage over iron-cored current measuring devices and these are well illustrated by considering how it can be used for measuring transient currents. The paper describes the principle of operation of Rogowski coils and the practical aspects of using them and gives several examples of their use in making transient measurements. The Rogowski coil is a conceptually simple device. Its theory of operation illustrates some basic principles of electromagnetism applied in a practical device. The coil itself provides an elegant demonstration of Ampere's Law and, because of its inherent linearity, the response of a coil under extreme measuring situations is much easier to treat theoretically than iron-cored measuring instruments. The educational aspects of studying Rogowski coils should not be overlooked.