  Scattered light echoes from variable and cataclysmic stars offer one of the
most effective means to probe the structure and composition of circumtellar and
interstellar media. I build a simple model of light-echo surface brightness by
considering the source spectrum, and the dust density, geometry, and scattering
efficiency. I use this model to investigate whether echoes should be observable
around short and long-period giants, cataclysmic variables, and supernovae.
Only supernovae are expected to illuminate material on both circumstellar and
interstellar scales. Giant and post-AGB stars (e.g. Cepheids and Miras) with
high mass-loss rates can produce observable echoes within their circumstellar
envelopes. Echoes from novae and dwarf novae are probably detectable only from
nearby material, and only in unusually dense gas. I present characteristic
exposure times to image such echoes over a wide range of wavelengths for
ground-based and {\em Hubble Space Telescope} observations. I apply these
results to analyze the dust properties of the recently-reported echoes around
SN 1993J, finding the dust in M81 to have a grain-size distribution and
chemical composition consistent with Galactic dust. Optimal observing
strategies for echo detection are also discussed.
