In tne last few decades new observational techniques have provided a wealth of physical information on several hundreds of asteroids. These objects are no longer seen as pointlike bodies
mainly interesting as a 'dynamical zoo', but have become small 'worlds' with known sizes, gross shapes, surface compositions, rotational properties and collisional histories. The diversity of these 'worlds' 3 is astonishing: they range in size from less than 1 to 10^3 km, in spin period from a few hours to many days, in shape from nearly spherical to very elongated and/or irregular, in surface reflectivity from about 0.02 .to 0.4, in composition from metal-rich and silicate rocks to volatile-rich carbonaceous assemblages. Of course there are many peculiar objects: asteroids with surface patches of different brightness and colour; bodies, which have suffered internal heating and have developed a core-mantlecrust
structure; asteroids converted by catastrophic impacts into gravitationally bound 'piles of rubble'; objects with triaxial equilibrium figures or splitted into binary systems; outer-belt
asteroids whose spectrophotometric properties are very much alike those of cometary nuclei. This paper reviews some of these recent findings, which are currently being interpreted in the frame of
complex theoretical models for the formation and evolution of orbiting and collisionally interacting bodies.