The envelope form may also be called a stamped envelope.
Postal services of some countries also offer a form of letter sheet called an aerogramme consisting of a blank sheet of paper with folding instructions and adhesive flaps that becomes its own envelope, and carries prepaid postage at the international airmail letter rate.
The first official postal stationery is the Mulready stationery that was issued by Great Britain at the same time as the Penny Black in 1840. Since then, most postal services have issued a steady stream of stationery alongside stamps; oftentimes the design of the stationery mimics the contemporaneous stamps, though with less variety and lower printing quality, due to the limitations of printing directly onto the envelope.
In emergency situations, postal stationery has been produced by handstamping envelopes with modified cancelling devices; many of the rare Confederate postmasters' provisionals are of this form.
Although the Scott catalog includes a section for United States postal stationery, and many other country-specific stamp catalogs describe the stationery of their respective countries, the 19-volume Higgins and Gage World Postal Stationery Catalogue is a main reference for stationery worldwide.
See also: stationery