There is described an envelope comprising rectangular front and back sheets joined on three sides to form a pocket, one of the sheets being provided with a flap foldable over the open side to close the pocket and form a first envelope. A part of the front panel adjacent to the open side is removable, with a corresponding part of the back panel remaining to form a second flap, foldable to close the pocket formed by remaining parts of the front and back panels so as to form a second, smaller, envelope. Further sections of the front and back panels may be removed, to leave a third pocket of even smaller size, with an open side which is closeable by a flap formed by a remaining part of the front or back panel so as to form a third envelope.