An Introduction to Scattered-Light Echoes

Scattered light echoes offer one of the most effective means to probe the structure and composition of circumstellar and interstellar media. Of note, light echoes provide exact three-dimensional positions of scattering dust. However, they are also very rare, and have only been unambiguously resolved around a handful of sources. I will discuss the history of light echo astronomy, and how they can be used to study the environments around variable stars and cataclysmic events. I will also show results from most of the existing known echo sources, showing how they have been used to map out star's circumstellar environments, probe the disks of galaxies, and determine the distance to variable stars.