The Boston Massacre, known in Great Britain as the Incident on King Street, was a confrontation, on March 5, 1770, during the American Revolution in Boston in what was then the colonial-era Province of Massachusetts Bay.

In the confrontation, nine British soldiers shot several in a crowd, estimated between 300 and 400, who were harassing them verbally and throwing various projectiles. The event was subsequently described as "a massacre" by Samuel Adams, Paul Revere, and other leading Patriots who later became central proponents of independence during the American Revolution and Revolutionary War. British troops had been stationed in the Province of Massachusetts Bay since 1768 in order to support Crown-appointed officials and to enforce unpopular legislation implemented by the British Parliament.

Amid tense relations between the civilians and the soldiers, a mob formed around a British sentry and verbally abused him. He was eventually supported by seven additional soldiers, led by Captain Thomas Preston, who were hit by clubs, stones, and snowballs. Eventually, one soldier fired, prompting the others to fire without an order by Preston. The gunfire instantly killed three people and wounded eight others, two of whom later died of their wounds.

The crowd eventually dispersed after acting governor Thomas Hutchinson promised an inquiry, but they reformed the next day, prompting the withdrawal of the troops to Castle Island. Eight soldiers, one officer, and four civilians were arrested and charged with murder, and they were defended in court by attorney, and future U.S. president, John Adams. Six of the soldiers were acquitted; the other two were convicted of manslaughter and sentenced to branding on the thumb, according to the law at that time.

Depictions, reports, and propaganda about the event, notably the colored engraving The Bloody Massacre, heightened tensions throughout the Thirteen Colonies.

In the 18th century, Boston was the capital of the Province of Massachusetts Bay, an important shipping town, and along with Philadelphia and present-day New York City, one of the most influential political, economic, and cultural cities in the Thirteen Colonies of pre-Revolutionary British America. Boston also was a center of resistance to unpopular acts of taxation by the British Parliament in the 1760s.

In 1768, the Townshend Acts were enacted in the Thirteen Colonies, placing tariffs on a variety of common items that were manufactured in Britain and imported in the colonies. Colonists objected that the Acts were a violation of the natural, charter, and constitutional rights of British subjects in the colonies. The Massachusetts House of Representatives began a campaign against the Acts by sending a petition to King George III asking for the repeal of the Townshend Revenue Act. The House also sent the Massachusetts Circular Letter to other colonial assemblies, asking them to join the resistance movement, and called for a boycott of merchants importing the affected goods.

Lord Hillsborough had recently been appointed to the newly created office of Colonial Secretary, and he was alarmed by the actions of the Massachusetts House. In April 1768, he sent a letter to the colonial governors in America instructing them to dissolve any colonial assemblies that responded to the Massachusetts Circular Letter. He also ordered Massachusetts Governor Francis Bernard to direct the Massachusetts House to rescind the letter, but it refused to comply.