  These lectures present some topics of string phenomenology and contain two
parts. In the first part, I review the possibility of lowering the string scale
in the TeV region, that provides a theoretical framework for solving the mass
hierarchy problem and unifying all interactions. The apparent weakness of
gravity can then be accounted by the existence of large internal dimensions, in
the submillimeter region, and transverse to a braneworld where our universe
must be confined. I review the main properties of this scenario and its
implications for observations at both particle colliders, and in
non-accelerator gravity experiments. In the second part, I discuss a simple
framework of toroidal string models with magnetized branes, that offers an
interesting self-consistent setup for string phenomenology. I will present an
algorithm for fixing the geometric parameters of the compactification, build
calculable particle physics models such as a supersymmetric SU(5) Grand Unified
Theory with three generations of quarks and leptons, and implement low energy
supersymmetry breaking with gauge mediation that can be studied directly at the
string level.
