The Somme offensive, also known as the battle of the Somme, is the term given to series of battles fought between 1 July and 18 November 1916 along the Somme Valley in France. It was the main Anglo-French offensive of 1916 and was originally planned as part of a wider strategy of attacking Germany simultaneously on the Western and Eastern Fronts, with the aim of destroying Germany's reserves of manpower. The massive German attack launched on the French fortress of Verdun on 21 February 1916 significantly reduced the French contribution, and the Somme offensive was partly intended to divert the German forces from Verdun.

The initial day of the offensive, 1 July 1916, remains the most costly day in the history of the British army. It suffered almost 60,000 casualties, a third of whom were killed, and the name "Somme" has become synonymous with slaughter. The attack on 1 July, and the operations that followed, were undermined by a failure to appreciate the strength of the German defences, and the relative ineffectiveness of the British artillery against them, and a lack of confidence in the abilities of Britain's volunteer army, which meant there was a distinct lack of imagination or innovation in the tactics employed.

When exhaustion, and the cloying mud of a particularly wet autumn, caused the offensive to be abandoned in November, the allied forces had managed to advance only 12 kilometres. The strategy of attrition upon which the offensive was founded proved a double-edged sword. It had resulted in around 500,000 German casualties, and the German army never recovered from its losses of experienced junior officers and NCOs on the Somme; however, this had come at a cost of 420,000 British and Dominion, and 200,000 French casualties. The offensive destroyed Britain's mass volunteer army, and for the rest of the war it would be reliant upon conscription for reinforcements

The major contribution of Australian troops to the Somme offensive was in the fighting around Pozieres and Mouquet Farm between 23 July and 3 September. Australian troops also launched several ill-conceived and ultimately futile attacks around Flers in November. Like their British allies, participation on the Somme put the first strain on Australia's voluntary recruitment system, and led to the first unsuccessful referendum to introduce conscription.