The Negroni is said to have originated in Italy, sometime in the early 1900s and as all good things, invented out of necessity. A local Italian bartender decided he needed to "strengthen" his Americano cocktail (not the coffee drink). He decided to add gin and a twist of orange in addition to the bitters and sweet vermouth.
Designed as an apertif, this beverage was thought to be good for the liver, and was consumed, before dinner, to "awaken the palate." It was a hit, and made famous all throughout Europe and across the Atlantic, here in the good old USA.
The bitter component now comes by way of Campari (Aperol is nice too) and is making a resurgence as a strong, balanced, subtle, and flavorful blast from the past.
1 part Gin
1 part Sweet Vermouth
1 part Campari
2 dashes citrus bitters
Twist of orange
Personally, I chill a martini or coupe-style glass with lots of ice while preparing the rest. Add a small handful of ice to your shaker/stirring pitcher and gin, vermouth, campari and your two dashes of bitters. Stir vigorously to get well incorporated and chilled. our into martini glass and garnish with orange peel. Enjoy!