Self-adhesive stamp

A self-adhesive stamp is a postage stamp with a pressure-sensitive adhesive that does not require moistening in order to adhere to paper. They are usually issued on a removable backing paper.
Stamp collectors criticized the format, because the rubber based adhesive used tended to progressively yellow the stamps. They also found them difficult to remove from covers, and to save in mint condition, though self-adhesives of recent years have improved in these respects.
Artistamps have also been issued in a self-adhesive format.
First adhesive stamps.
They were first issued by such tropical climates as Sierra Leone in February 1964 and Tonga in April 1969 in an attempt to avoid the tendency of traditional water-activated stamps to stick together in humid conditions. They also made die cutting into fanciful and unique shapes easier.
In the UK.
The British Post Office first issued self-adhesive stamps on 19 October 1993, with the introduction of books of 20 first class stamps, later a second class stamp was introduced. In later years other issues were produced in the self-adhesive format.
Die cutting tools for the UK self adhesive stamps were manufactured by Arden Dies of Stockport, Cheshire using tools designed by Robert Clapham. 
In the US.
The United States Postal Service's first foray into self-adhesive stamps was in 1974 with the 10-cent dove weathervane, produced by Avery Dennison, that soon became discolored due to the instability of the adhesive. However, Avery Dennison continued adhesive technology research with pioneering work by M. Shams Tabrez, a chemist. It was in 1989 that another such self adhesive stamp was issued by the USPS. Outside of the philatelic community, the stamps have been welcomed as more convenient; by 2002, virtually all new USPS stamps were issued as self-adhesives.
More recent USPS self-adhesive stamps are not readily removable from the envelope or cover backing by traditional water soaking. Some collectors of used stamps have discovered that although not readily removable by water, the self-adhesives can be removed with Bestine (a heptane solvent), benzine (petroleum ether), or a natural based citrus solvent containing d-limonene (e.g., Pure Citrus Orange is an air freshener product that works for this purpose).