These four lectures are meant as an elementary introduction to the physics of realistic supersymmetric models. In the first lecture, after reviewing the motivations for low-energy supersymmetry and the recipe for the construction of supersymmetric lagrangians, we introduce the Minimal Supersymmetric extension of the Standard Model, and comment on possible alternatives. In the second lecture, we discuss what can be learnt by looking at such model as the low-energy limit of some unified theory, with emphasis at the implications of its renormalization group equations and at the possibility of a supersymmetric Grand Unification. The third lecture is devoted to the problem of supersymmetry breaking: we review some general features of the spontaneous breaking of global and local supersymmetry, and we compare the supergravity models with heavy and light gravitino. In the fourth lecture, we conclude with an overview of supersymmetric phenomenology: indirect effects of supersymmetric particles in electroweak precision tests and in flavour physics, as well as direct searches for the superpartners of ordinary particles.