A blue law in the United States refers to laws restricting activities or sales of goods on Sunday, to accomdate the Christian "sabbath."

The term blue law was first used by Reverend Samuel Peters in his book General History of Connecticut, which was first published in 1781, to refer to various laws first enacted by Puritan colonies in the 17th century which prohibited the selling of certain types of merchandise and retail or business activity of any kind on certain days of the week (usually Sunday). In Texas, for example, blue laws prohibited selling housewares such as pots, pans, and washing machines on Sunday until 1985, and many southern states still prohibit selling alcohol on Sunday. Many unusual features of American culture -- such as the fact that one can buy groceries, office supplies, and housewares from a drug store -- are the result of blue laws, as drug stores were allowed to remain open on Sunday to accommodate emergency medical needs.

Contrary to popular belief, there is no evidence to support the assertion that the blue laws were originally printed on blue paper. Rather, the word blue was commonly used in the 18th century as a disparaging reference to rigid moral codes and those who observed them. To wit, "bluenoses". Moreover, although Reverend Peters claimed that the term blue law was originally used by Puritan colonists, his work has since been found to be unreliable,more likely that he simply invented the term himself. In any event, Peters never asserted that the blue laws were originally printed on blue paper.

It is likely that all blue law stems from the first such statute set down by the Emperor Constantine 1300 years before the Puritans:

"Let all judges and all city people and all tradesmen rest upon the venerable day of the sun. But let those dwelling in the country freely and with full liberty attend to the culture of their fields; since it frequently happens that no other day is so fit for the sowing of grain, or the planting of vines; hence, the favorable time should not be allowed to pass, lest the provisions of heaven be lost." -- Given the seventh of March, Crispus and Constantine being consuls, each for the second time. A.D. 321.