An infrared spatial interferometer has achieved an order-of-magnitude improvement in the angular resolution of ground-based telescopic observations at wavelengths from 2.2 to 20μm. Using incoherent detectors to measure fringe visibility versus baseline, this instrument has obtained an effective angular resolution of 0.1 arcsec at 10.2μm with a 3.2m baseline in 3 arcsec conditions of visual atmospheric "seeing". Observations are made at eight wavelengths to probe different levels of temperature and density in circumstellar envelopes. Twenty-three stars of various spectral types are partially resolved and upper limits placed on the sizes of 25 others. Three stars contain flattened, disk-shaped envelopes. At 10.2μm, objects as faint as zero magnitude have been measured. Significant improvements in sensitivity are expected using a composite diamond-germanium bolometer operating under low background conditions and cooled to 0.3K in a newly developed He3 cryostat. Angular resolution can be doubled using a ≥6.5m baseline provided by the Multiple Mirror Telescope. Plans to use the MMT as a multi-element spatial interferometer will be discussed.