Resonances play a very relevant role in the dynamical behaviour of the small bodies of the Solar System. Some resonances act as protection mechanisms from close encounters with the perturbing planets, while some others pump the eccentricity of resonant bodies and force them to encounter the planets; finally some resonances have a very complex dynamics, characterized by slow diffusion of orbital elements.
We will show the main effects of resonances in the asteroid belt, in the Kuiper belt and in the evolution of NEAs, and we will discuss the open problems (with astronomical implications) that still persist in resonant dynamics.