The Keystone View Company was formed by B. L. Singley in 1892 in Meadville, Pennsylvania to produce and sell stereoview cards, becoming the largest producer of stereoviews by 1905 at which point it offered 20,000 different views and also started selling educational lantern slides.
Most of their stereview cards were, like other stereoviews, two photographs mounted on card that when viewed with a stereoscope viewer produced a 3D effect. Keystone also produced the cheaper Keystone Junior stereographs that were much smaller images on photographic paper without the cardboard backing.
Between 1915 and 1921, the Keystone View Company bought the negatives of most of the their competitors, including Underwood & Underwood. The Keystone View Company was bought by Mast Development Company in 1963 and finally ceased distribution of stereoviews.
In 1978, the Keystone View Company’s negatives and prints were donated to the University of California and formed the Keystone-Mast collection of around 350,000 prints and original glass and film negatives, some of which is now available online.