The appearance of the envelope filled a practical as well as a market need. Soon, the people who wanted to send letters had to buy the paper and also the envelope so as to be able to send the letter. It is interesting therefore that the standard envelope has a relatively late development. Even more recent is the invention of the window envelope which is only one hundred years old and who was first patented by Americus F. Callahan at the beginning of the twentieth century: "Standard sized pre-cut and pre-gummed envelopes only became common in the nineteenth century. And on June 10, 1902, window envelopes were first patented by a man named Americus F. Callahan of Chicago." The window- envelopes, that is, the envelopes which have a special transparent window through which the address written on the letter can be well seen are today the most widely used type of envelope. These envelopes serve now for the purpose of all the official mail, including billing and other information which needs to be sent out by post. In time however, the envelope and the stamps began to vary according to their purpose and their destination. The colors, the type of paper and the size were multiplied and made to suit a variety of needs. The envelope has nevertheless preserved the initial design. It is usually rectangular in shape, flexible, and has a flap with an adhesive band that seals the letter. In the United States, standard sizes can be from 3.5 x 6 in (89 x 152 mm) to 10 x 13 in (254 x 330 mm). In Europe, sizes range from 3.2 x 4.5 in (81 x 114 mm) to 11 x 15.75 in (280 x 400 mm). Nowadays, the envelopes are usually covered with a print, with images and special marks for placing the stamp or address. While the initial standard pattern has not changed very much, the window envelopes are the most used type of cover available.

The modern technology of communication offers a variety of mailing possibilities which have significantly decreased the paper-based correspondence. However, official information and billing is still widely sent out by mail so the envelope still plays a major role in the postal services. The evolution of the envelope from a home made utility to a standard, marketable product is significant as it points to the general pattern associated with the history of civilization. Thus, while in the beginning of history communication was a severely limited to very small area, with time, the need and the possibilities for communication expanded significantly. The appearance of paper and especially of wood-manufactured paper contributed significantly to the development of communication and later of printing. As such, it was no longer convenient for people to manufacture their own envelopes, and the need for a standard pattern was felt. The historical evolution of the envelope thus coincides with the evolution of human civilization itself.
Works Cited

The Envelope." How Products are Made. http://www.madehow.com/Volume-5/Envelope.html

The History of the Envelope." Royal Envelope. http://www.royalenvelope.com/history/

Healy, Barth. Stamps. An Envelope's History Lies in the Fine Print. http://query.nytimes.com/gst/fullpage.html?res=9F0CEEDD1630F932A15751C0A965958260

Today in Technology History." The Center for the Study of Technology anc Society. http://www.tecsoc.org/pubs/history/2002/jun10.htm

The Envelope." How Products are Made. http://www.madehow.com/Volume-5/Envelope.html