A stereoscope is a device for viewing stereographic cards, which are cards that contain two separate images that are printed side-by-side to create the illusion of a three-dimensional image. This is the oldest method of stereoscopy, having been discovered in the mid-19th century by Charles Wheatstone.

In the late 19th and early 20th century "stereoviews", stereo cards, stereo pairs or stereographs were popularly sold. The cards had a pair of photographs, usually taken with a special camera that took the pair of images from slightly separated views simultaneously. Cards were printed with these views (often with explanatory text); when the cards were looked at through the double-lensed viewer, called a stereoscope or a stereopticon (a common misnomer), a three-dimensional image could be seen.