Abstract

Circumstellar disks appear in the early phases of formation of stars and play a key role in the assembly of the final mass of the central star and in the possible formation of a planetary system around it. I will review our understanding of the properties and evolution of disks around young stellar objects, focusing on the solids (dust and pebbles) in disk. The evolution of the solids is directly related to the initial stages of planets formation as grains are expected to grow to large pebbles and form first planetesimals and then rocky cores of planets. I will discuss the current observational evidence for grain evolution in disks, the difficulties and successes of theoretical models to explain observations and the latest ideas on grain populations segregation in disks. I will discuss future observational tests, in particular with ALMA Early Science and beyond, that will allow us to pose tighter constraints on models of solids evolution in disks.