Infrared spatial interferometry of red giant stars is a powerful way to study the distribution of gas and dust in the circum-stellar envelopes. The circumstellar dust around many giant stars is easily resolved at infrared wavelengths. The dust distributions sometimes deviate markedly from spherical and even reflection symmetry in the objects most easily resolved. The light intensities suggest dust formation radii larger than expected on the basis of pure theory, and may mean that mass loss is not driven by radiation pressure on dust grains, although there are different interpretations. Radial density and temperature distributions expected for uniformly outflowing envelopes heated solely by the central stars are consistent with the observed emission sizes versus wavelength, but are not strongly constrained by the data.
