  We report on our project of coordinated VLTI/VLBA observations of the
atmospheres and circumstellar environments of evolved stars. We illustrate in
general the potential of interferometric measurements to study stellar
atmospheres and envelopes, and demonstrate in particular the advantages of a
coordinated multi-wavelength approach including near/mid-infrared as well as
radio interferometry. We have so far made use of VLTI observations of the near-
and mid-infrared stellar sizes and of concurrent VLBA observations of the SiO
maser emission. To date, this project includes studies of the Mira stars S Ori
and RR Aql as well as of the supergiant AH Sco. These sources all show strong
silicate emission features in their mid-infrared spectra. In addition, they
each have relatively strong SiO maser emission. The results from our first
epochs of S Ori measurements have recently been published and the main results
are reviewed here. The S Ori maser ring is found to lie at a mean distance of
about 2 stellar radii, a result that is virtually free of the usual uncertainty
inherent in comparing observations of variable stars widely separated in time
and stellar phase. We discuss the status of our more recent S Ori, RR Aql, and
AH Sco observations, and present an outlook on the continuation of our project.
