Henry V of England invaded France following the failure of negotiations with the French. He claimed the title of King of France through his great-grandfather Edward III, although in practice the English kings were generally prepared to renounce this claim if the French would acknowledge the English claim on Aquitaine and other French lands (the terms of the Treaty of Brétigny). By 1415 negotiations had ground to a halt, with the English claiming that the French had mocked their claims and ridiculed Henry himself. In December 1414, the English Parliament was persuaded to grant Henry a "double subsidy", a tax at twice the traditional rate, to recover his inheritance from the French. On 19 April 1415, Henry again asked the great council to sanction war with France, and this time they agreed.

On Tuesday 13 August 1415, Henry landed at Chef-en-Caux in the Seine estuary. Then he attacked Harfleur with at least 2,300 men-at-arms and 9,000 bowmen. The defenders of Harfleur surrendered to the English on terms and were treated as prisoners of war. The English army was considerably reduced by casualties and an outbreak of dysentery during the siege but marched towards Calais, leaving a garrison behind at the port.