The am­per­sand is ty­po­graphic short­hand for the word and. The am­per­sand is halfway be­tween a lig­a­ture and a con­trac­tion —it’s a styl­ized de­pic­tion of the Latin word et.

The am­per­sand is one of the jaun­ti­est char­ac­ters. Font de­sign­ers of­ten use it as an op­por­tu­nity to show off. Tra­di­tional am­per­sands take the shape of the let­ters et. Mod­ern am­per­sands are of­ten more stylized.

Am­per­sands are com­pletely cor­rect when they’re part of a proper name (Fro­mage & Cra­cotte LLP).

Oth­er­wise, am­per­sands should be han­dled like any other con­trac­tion: the more for­mal the doc­u­ment, the less they should be used. Here and there, but not everywhere.