An Envelope is a flat paper or cardboard container consisting of a pocket and a flap with an adhesive. It protects documents and provides privacy when sending them in the mail. The recipient's address should be written in the center or upper right corner of the envelope, and the return address should be written in the upper left corner.

The first envelopes were used by the Babylonians in 2000 BC. They were made of clay and applied by folding wet clay over the documents and baking them. They were used to protect important documents, but were not very efficient as the clay envelope had to be broken in order to get to the document. Paper became common in the 10th century, and the governmental postal systems available in 15th century. Envelopes naturally came along. In the 1840s Edwin Hill and Warren de la Rue began using a steam-powered machine that would cut and fold envelopes. Before this all envelopes were made by hand.