My research has mostly dealt with the theory and the phenomenology of the fundamental in- teractions, motivated by the desire to understand, within a consistent theoretical framework, the mass generation for the weak gauge bosons, the quarks and the leptons, and the possi- ble unification of gravity with the other forces at the quantum level. I have been focusing on theoretically motivated extensions of the Standard Model, with emphasis on those based on supersymmetry, supergravity and superstrings. On the one hand, I have been pushing further the confrontation of the existing models with experiment, identifying new features and possible tests at contemporary and future experimental facilities. On the other hand, I have been ex- ploring how some long-standing theoretical problems (the gauge hierarchy problem, the flavour problem, the cosmological constant problem, and others) may be addressed in the framework of superstring theories and their effective supergravity theories in four and higher dimensions.