In the first lecture, the Standard Model is reviewed, with the aim of seeing how its successes constrain possible extensions, the significance of the apparently low Higgs mass indicated by precision electroweak experiments is discussed, and defects of the Standard Model are examined. The second lecture includes a general discussion of the electroweak vacuum and an introduction to supersymmetry, motivated by the gauge hierarchy problem. In the third lecture, the phenomenology of supersymmetric models is discussed in more detail, with emphasis on the information provided by LEP data. The fourth lecture introduces Grand Unified Theories, with emphases on general principles and on neutrino masses and mixing. Finally, the last lecture contains s...