Planetary systems form out of disks of gas and dust around young stars. How the formation proceeds, however, is complex and poorly understood. Many physical processes are involved including accretion onto the star, photoevaporation of material of the disk, interactions of the disk with planetary embryos, growth of the dust grains, settling of the dust to the midplane of the disk, and more. To unravel these various factors, observations of protoplanetary disks at multiple wavelengths are used; the submillimeter wavelength range in particular offers a way to peer through most of the disk to estimate dust masses directly.