The ampersand, also known as the and sign, is the logogram &, representing the conjunction "and". It originated as a ligature of the letters et—Latin for "and".

Traditionally in English, when spelling aloud, any letter that could also be used as a word in itself ("A", "I", and "O") was referred to by the Latin expression per se ('by itself'), as in "per se A" or "A per se A". The character &, when used by itself as opposed to more extended forms such as &c., was similarly referred to as "and per se and". This last phrase was routinely slurred to "ampersand", and the term had entered common English usage by 1837.

It has been falsely claimed that André-Marie Ampère used the symbol in his widely read publications and that people began calling the new shape "Ampère's and".

The ampersand can be traced back to the 1st century AD and the old Roman cursive, in which the letters E and T occasionally were written together to form a ligature. In the later and more flowing New Roman Cursive, ligatures of all kinds were extremely common. During the later development of the Latin script leading up to Carolingian minuscule (9th century) the use of ligatures in general diminished. The et-ligature, however, continued to be used and gradually became more stylized and less revealing of its origin.

The modern italic type ampersand is a kind of "et" ligature that goes back to the cursive scripts developed during the Renaissance. After the advent of printing in Europe in 1455, printers made extensive use of both the italic and Roman ampersands. Since the ampersand's roots go back to Roman times, many languages that use a variation of the Latin alphabet make use of it.

The ampersand often appeared as a character at the end of the Latin alphabet, as for example in Byrhtferð's list of letters from 1011. Similarly, & was regarded as the 27th letter of the English alphabet, as taught to children in the US and elsewhere. An example may be seen in M. B. Moore's 1863 book The Dixie P