We consider the current state of star-formation theory and requirements for millimeter and submillimeter observations that would enable the resolution of the most pressing problems in the physics of star formation. Two key features of star-forming regions that define these observational requirements are the relatively low energy of processes taking place there and the smallness of the corresponding spatial scales. This is especially true for objects in the latest stages of “pre-stellar” evolution, that is, hot cores, hypercompact and ultracompact HII regions, and protoplanetary disks. The angular resolution, sensitivity, and spectral coverage in existing ground-based and space submillimeter and millimeter telescopes are not fully adequate to the observtional requirements. To obtain detailed information on star-forming regions, as well as individual protostars, it is necessary to use a space-based interferometer.