  This paper will review the technical progress of interferometric infrared
observing techniques from the first 2-element interferometer 25 years ago to
the 3+ element arrays now coming into service. To date, only the Infrared
Spatial Interferometer (ISI) has published separate-element interferometric
data on circumstellar dust shells in the infrared and many of these scientific
results will be discussed. Speckle interferometry has also evolved
significantly over the last few decades as slit-scanning techniques over
single-pixel detectors have largely been replaced by fast-readout of large
format detector arrays. Important near-infrared and mid-infrared results
derived from speckle data will also be reviewed.
  Until recently, two-dimensional information about circumstellar dust
distributions has been sorely lacking, hence detections of dust shell
asymmetries have been difficult and uncertain. New speckle observations using
modern, 10-m class telescopes have yielded surprising results, demonstrating
the importance of accurate closure phase information in interpreting
interferometric data. These discoveries hopefully precursor those to be made
from closure-phase imaging with the new generation of separate-element,
interferometric arrays.
