Unification in particle physics: Symmetries and hidden dimensions

The properties of matter at the atomic level are expressed in terms of a few fundamental constants, while, going down to the level subnuclear constituents, the present theoretical description requires the introduction of a large number of independent parameters. The main goal of elementary particle physics is to arrive at a complete theory which describes all subnuclear phenomena in terms of a unified interaction with the least number of fundamental constants. We discuss the lines of research in this field, which are mainly based on the implementation of higher symmetries. Grand Unified Theories unify the couplings of the fundamental interactions and, with the implement of family symmetry, some of the parameters of the basic fermions become related. Supersymmetry is an essential ingredient of the present theories and the introduction of hidden space-time dimensions appears to be a common feature. The gravitational interaction plays an important role in the unifying picture, linking low-energy parameters with the physics at the Plank scale.