Asteroids can be defined as objects that do not have an atmosphere, are smaller than the planets and orbit the Sun. But, what is most important, asteroids are the remnants of the first forming blocks of the Solar System. The main asteroid population is located between the orbits of Mars and Jupiter, in a region called the Main Belt (MB). Other important populations are near-Earth asteroids (NEAs) and Mars crossers (MCs). In the outer Solar System, cold, icy bodies that are located beyond the orbit of Neptune are called trans-neptunian objects (TNOs), and concentrate in a region known as the Kuiper Belt. Visible and near-infrared reflectance spectra of all these ``minor bodies'', obtained from ground-based observations, are modelled using different techniques, and, together with laboratory experiments with analogue materials (both terrestrial and from meteorites), they allow us to infer information about several properties, like surface composition, particle size distribution or the effects of space weathering. The analysis of the physical and dynamical properties of these objects, as well as their surface composition is of particular interest, as it is fundamental to understand the processes involved in the formation and subsequent evolution of the Solar System.