It is usually a thin rod bent into a looped shape that takes advantage of the flexibility and strength of the materials of its construction (usually some sort of metal, but sometimes plastic) to compress and therefore hold together two or more pieces of paper.
The most common type of wire paper clip was never patented, but it was probably in production in Britain as early as 1890 by "The Gem Manufacturing Company". A machine for making Gem-type paper clips was patented in 1899 by William Middlebrook of Waterbury, Connecticut. They are still sometimes called "Gem clips", and in Swedish, the word for any paper clip is "gem". Byzantines are thought to have originally invented a paper clip which was fashioned from brass. However, this proved too costly to produce in large numbers, and was only used for binding highly valued imperial documents.
A Norwegian, Johan Vaaler, patented a less functional version in 1899 and 1901, but it was never manufactured because a better product already existed. Most literature usually but falsely credits him with the invention of the Gem-type clip. Awareness that a Norwegian had invented some kind of paper clip gave rise to the persistent myth that the paper clip was a Norwegian invention. This contributed to the widespread use of paper clips as a symbol of resistance to the German occupiers and local Nazi authorities during World War II. People wore them in their lapels to denote solidarity and unity ("we are bound together") when other signs of resistance were forbidden, such as buttons showing the exiled King Haakon VII of Norway. A giant paper clip was erected near Oslo in honour of Vaaler.
Despite hundreds of variations, the original design is still the most popular. Its qualities of easy use, gripping without tearing, and storing without tangling have been difficult to improve on.
A paper clip is also a useful accessory in computing: the metal wire can be unfolded with a little force. Several devices call for a very thin rod to push a recessed button which the user might only rarely need. This is seen on most CD-ROM drives as an "emergency eject" should the power fail; also on early disk drives (including the early Macintosh). Some Palm PDAs advise the use of a paper clip to reset the device.
Other paper-fastening devices:
Microsoft infamously introduced a cartoon character shaped like a paper clip in their Office 97 software suite, nicknamed "Clippit". It was intended to deliver useful information to users as an active help procedure, but it was largely perceived as an irritation by users, and became the subject of many parodies. In newer versions of the software, it is switched off by default. User agent technology creating characters such as Clippy were already present in Microsoft's "Bob" project (which most regard as having failed).
- Henry Petroski, The Evolution of Useful things (1992); ISBN 0679740392 (a history of the evolution of paper clip design)
- US3057027 — Paper clip — E. P. Bugge