The circumstellar disks that naturally arise from the star formation process are the sites where planets are made. Gravitational, hydrodynamic, magnetic, and chemical processes are all active in determining the evolution of these disks and their planet forming activity. I will review recent progress in understanding "protoplanetary" disks through observations at millimeter and submillimeter wavelengths. With typical temperatures of 20 to 100 K within a few 100s of AU from young Sun-like stars, the disk material is cold, and this spectral region is rich in diagnostic probes. Solids are accessible through thermal continuum emission, and gas kinematics and chemical properties are studied through resolved images of line emission from trace molecular species. Several interferometers, including the SMA and VLA, allow for imaging observations at Solar System size scales, in some cases reaching the Jovian orbit scale. The dust emission is almost entirely optically thin and allows for direct tests of physical models of disk structure. The detailed study of these disks is a key science driver for ALMA, with increases in sensitivity and resolution that should revolutionize this field.