The rules of fashion dictate how women should dress to suit the time of day, season, social occasion, or activity. They influence colors, materials, necklines, hemlines, and other elements of fashionable dress. Sometimes they operate as a flexible set of guidelines, at other times as strictly observed etiquette that is continually reinforced in the fashion press. Since the early nineteenth century, women’s clothing has been primarily divided into daywear and eveningwear, categories that are governed by specific dress codes. Night & Day explores the evolution of the rules that have governed fashion over the past 250 years, revealing when they have been at their most extreme or so relaxed as to be barely perceptible.