Abstract: The mechanism, characteristics, primary applications, background, and latest research on the tunnelling magnetoresistance effects of magnetic tunnel junctions (MTJs) are reviewed. Different types of junctions with Al2O3 or MgO insulated barriers are compared, and the merits of the MgO barrier discussed. The problems and disadvantages of exchange-biased spin-valve MTJs as well as the advantages of the promising pseudo-spin-valve junctions are illustrated. Finally, a summary of the materials used for the ferromagnetic layer and insulated barrier is given, and the outlook for further research and development of tunnelling magnetoresistance materials is discussed.