The largest German producer of World War stereoviews was Neue Photographische Gesellschaft (NPG), Berlin. The company produced standard-size stereoviews on photo paper for the German and Austro-Hungarian markets. NPG sold several images to American companies during and after the war. The other major German producer was Feldstereo-Verlag, Frankfurt a. Main, which sold small-format paper stereoviews with a proprietary cardboard viewer. Neither company is known to have produced glass stereoviews.