What glass should I use for a Negroni?

A rocks glass (old-fashioned glass, double old-fashioned, or lowball — all the same thing) with one large ice cube. Coupe glasses also work if you prefer the drink served up.

The canonical Negroni glass is the rocks glass, a short heavy-bottomed tumbler holding 8 to 12 ounces. The Negroni is served over a single large ice cube — ideally 2 inches square — to minimize dilution while keeping the drink very cold. Why the rocks glass: the wide mouth lets the bitter aromatics rise; the short, heavy form fits in the hand and feels right for a slow-sipped pre-dinner drink. Coupe (up): some Italian bars and many American craft bars serve the Negroni in a coupe with no ice, strained from a chilled mixing glass. This is correct historically — pre-Prohibition Negronis were often served up — but the modern standard is rocks. The 'on the rocks' version dilutes slightly more over the course of the drink, which is part of the Negroni's evolution in the glass: bitter and sharp on the first sip, smoother and more balanced by the third. If you don't have a rocks glass, a small wine glass also works; avoid using a martini glass (too narrow at the top, oddly proportioned for the drink's heft).