Writs of Assistance, in United States colonial history, general search warrants used by British customs officers to prevent smuggling. The use of these writs was one of the grievances of the colonists before the Revolutionary War.

For years the British government had tried to prevent the colonies from trading with lands outside its control. The Molasses Act of 1733 levied a heavy duty on certain products from foreign lands. Widespread smuggling made this act almost meaningless. Britain spent about $8,000 a year to collect $2,000 in duties.

Customs officials first used specific warrants that described the places to be searched. These warrants were ineffective. The government then authorized use of general writs permitting the search of any house or ship. These writs were first used in Massachusetts in 1751 without causing trouble. When George III became king in 1760, new writs had to be issued in his name. In 1761 British officials in Boston applied for the writs. James Otis, a fiery and eloquent lawyer, opposed issuance of these writs. He argued that the act of Parliament authorizing writs of assistance was contrary to the British common law, and therefore was void.

Otis made a brilliant speech but he lost his case, and the writs were issued in Massachusetts. Later, however, courts in some of the other colonies refused to issue general search warrants. John Adams, who heard the speech of Otis, wrote of it many years afterwards: "Then and there, the child Independence was born."