Phantasmagoria (American pronunciation , also fantasmagorie, fantasmagoria) was a form of horror theatre that (among other techniques) used one or more magic lanterns to project frightening images, such as skeletons, demons, and ghosts, onto walls, smoke, or semi-transparent screens, typically using rear projection to keep the lantern out of sight. Mobile or portable projectors were used, allowing the projected image to move and change size on the screen, and multiple projecting devices allowed for quick switching of different images. In many shows, the use of spooky decoration, total darkness, (auto-)suggestive verbal presentation, and sound effects were also key elements. Some shows added a variety of sensory stimulation, including smells and electric shocks. Such elements as required fasting, fatigue (late shows), and drugs have been mentioned as methods of making sure spectators would be more convinced of what they saw. The shows started under the guise of actual séances in Germany in the late 18th century and gained popularity through most of Europe (including Britain) throughout the 19th century.

The word "phantasmagoria" has also been commonly used to indicate changing successions or combinations of fantastic, bizarre, or imagined imagery.