Submillimeter studies of circumstellar disks in Taurus and Orion

We highlight two recent studies of circumstellar disks in the Taurus and Orion star forming regions. Using the JCMT and CSO, we measure disk fluxes in Taurus over a wide range of submillimeter wavelengths and determine the frequency dependence of the dust opacity. We find clear evidence for a systematic change in its behavior with time, most readily explained by grain growth. Using the SMA, we observed the protoplanetary disks (proplyds) in the Orion Trapezium cluster. The combination of high resolution, high frequency, and high sensitivity that this instrument provides made it possible to resolve disks from one another, distinguish their emission from background cloud material and surrounding ionized gas, and to detect thermal dust emission. This allowed us to make the first mass measurements of the proplyds and to assess their viability for planet formation.