Orange bitters are a type of cocktail bitters made from the peels of bitter oranges, along with various herbs, spices, and other flavoring agents. They are used to enhance the flavor of cocktails and can add a complex, citrusy note to drinks. Originally developed in the 19th century, orange bitters were a popular ingredient in classic cocktails like the Old Fashioned and the Manhattan. Today, they are still used by bartenders to balance sweetness and add depth to various mixed drinks.