Abstract
Molecular clouds, the cradle of star formation, form self-similar structures over a wide range of scales. They are lumps and filaments between the size of the Solar System and hundreds of light-years. This hierarchy of structures, subject to gravity but stabilized by turbulence and magnetic fields, will collapse into cold cores, then into stars, at the center of a protostellar disk, then protoplanetary, where embryonic planets are born. The physics of these processes is revealed by increasingly powerful observations with telescopes in space (HST, JWST) or on the ground (ALMA).
