We propose a program of high angular resolution imaging of the thermal emission from cool dust around a selection of pre-main-sequence young stars. These observations will be used to constrain the contribution from extended envelope emission to the total thermal dust emission from the stars. Work in our group and by collaborators using the Kuiper Airborne Observatory has shown that the far-infrared is a senstive region for detecting envelope emission. We have also shown that many brighter pre-main-sequence stars have extensive envelopes which call into question the inference of circumstellar disks based solely on spectral energy distributions. In this ISO proposal we plan to extend this research to fainter and lower luminosity sources, as well as to a broader range of stellar types. With these data we will have a much more complete picture of the relationship of envelope contribution to disk contribution over a range of stellar luminosity from a few solar luminosities to a few thousand solar luminosities.