The formation of stars and planets is a crucial part of the process that leads from the expanding universe to the presence of sites for life. While much progress has been made in understanding star and planet formation over the last several decades, our understanding is still quite primitive. The Spitzer Space Telescope (SST) is providing dramatic improvements in our observatational capabilities in the infrared region. This telescope was launched August 2003, and one of the key (Legacy) programs addresses star and planet formation. This program, `From Molecular Cores to Planet-forming Disks (c2d)', has Neal Evans as the PI and Ewine van Dishoeck as one of 10 co-Is. The proposal that led to this program was planned and largely written during a workshop at the Lorentz Center in summer of 2000. Now we propose to return to the Lorentz Center in the summer of 2005 to discuss the scientific results and work on papers that will present these results.
Among the scientific questions to be addressed are the following. What are the steps and the timescales involved in turning a core of molecular material into a star and planets? What is the location of formation of stars of various masses? What is the relative importance of isolated and clustered star formation for different mass ranges? Which, if any, of the current theories of star formation provide a good explanation of the observations? What is the incidence of extra-solar planetary systems and what are the steps that lead to them? How is the outcome (number and location of planets) related to the physical conditions in the protoplanetary disk? How does the composition of dust and gas change during the process of star and planet formation?