In these lectures, the confinement principles of the tokamak are outlined and the present status of tokamak research is reviewed, with particular reference to the JET machine, which is the largest operating tokamak in the world. The need for additional heating in tokamaks is discussed and the various methods are compared. Certain parameter limitations (e.g. disruptions, sawtooth oscillations, impurities and a limits) presently encountered are detailed and options for surmounting these problems are presented. Their effect on energy confinement and the various empirical scaling laws encountered in differing conditions are discussed, particularly the confinement degradation observed in additional heating situations. Finally, the main achievements and future outlook with tokamaks are summarised.