Testing strings at the LHC

I discuss the main motivations and directions for physics beyond the Standard Model of elementary particles and I give a short introduction on string theory. This theory introduces a new physical constant, the string length, under which a new fundamental structure appears, changing drastically the laws of nature. In particular, lowering the string scale in the Te V region provides a theoretical framework for solving the so-called mass hierarchy problem: the apparent weakness of gravity can be accounted by the existence of large internal dimensions, in the submillimeter region, and transverse to a braneworld where our observed universe is confined. In these lectures, I describe the main properties of string phenomenology with high or low string scale. In the latter case, I discuss also its implications for new gravitational phenomena that can be observed at both particle colliders, and in non-accelerator experiments searching for new short range forces.