Scattered light echoes offer one of the most effective means to probe the structure and composition of circumtellar 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 almost all of the known echo sources, including SN 1987A, whose echoes have produced the first 3-D map of a high-mass star's mass-loss history.