Sumptuary laws (from Latin sūmptuāriae lēgēs) are laws that regulate consumption. Black's Law Dictionary defines them as "Laws made for the purpose of restraining luxury or extravagance, particularly against inordinate expenditures for apparel, food, furniture, or shoes, etc." Historically, they were intended to regulate and reinforce social hierarchies and morals through restrictions on clothing, food, and luxury expenditures, often depending on a person's social rank.

Societies have employed sumptuary laws for various purposes. They were used to try to regulate the balance of trade by limiting the market for expensive imported goods. They made it easy to identify social status and privilege, and as such could be used for social discrimination and to stabilize social hierarchies. They could also be used to prevent, or at least reduce, opportunities for political bribery and corruption.

The laws often prevented commoners from imitating the appearance of aristocrats, and could be used to stigmatize disfavoured groups. In cities of the Late Middle Ages, sumptuary laws were instituted as a way for the nobility to limit the conspicuous consumption of the prosperous bourgeoisie. Bourgeois subjects as wealthy as or wealthier than the nobility could undermine the latter's presentation as powerful and legitimate rulers. This could call into question their ability to control and defend their fiefs, thus inspiring traitors and rebels. Such laws continued to be used for these purposes well into the 17th century.

According to historian Lorraine Daston, sumptuary laws "furnish the historian of rules with an extreme case of rule failure," as such laws frequently failed to reduce excess and may even have exacerbated excess. Sumptuary laws were often revisable regulations rather than stable laws, as governing authorities sought to prohibit the latest rebellious or extravagant fashions.

The 7th century BCE law text of the Locrians by Zaleucus, the first written code of law in ancient Greece, stipulated:

A free-born woman may not be accompanied by more than one female slave, unless she is drunk; she may not leave the city during the night, unless she is planning to commit adultery; she may not wear gold jewelry or a garment with a purple border, unless she is a courtesan; and a husband may not wear a gold-studded ring or a cloak of Milesian fashion unless he is bent upon prostitution or adultery.

It also banned the drinking of undiluted wine except for medical purposes.

The Sumptuariae Leges of ancient Rome were various laws passed to prevent inordinate expense (Latin sūmptus) in banquets and dress, such as the use of expensive Tyrian purple dye. Roman senators and senior magistrates were entitled to wear a Tyrian purple stripe on their toga and tunic. In the early years of the Roman Empire, men were forbidden to wear silk, which was deemed an effeminate and morally suspect material. During the height of the Empire, expenditure on silk imported from China was so high that imperial advisers warned that Roman silver reserves were becoming exhausted.