Toughened or tempered glass is glass that has been processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. It will usually shatter into small fragments instead of sharp shards when broken.

The first patent on tempered glass was held by chemist Rudolph A. Seiden, born in 1900 in Austria.

Though the underlying mechanism was not known at the time, the effects of "tempering" glass have been known for centuries. In the 1640s, Prince Rupert of Bavaria brought the discovery of what are now known as "Prince Rupert's Drops" to the attention of the King. These are teardrop shaped bits of glass which are produced by allowing a molten drop of glass to fall into a bucket of water, thereby rapidly cooling it. The teardrops were often used by the King as a practical joke.

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