A war hammer is an archaic weapon of war intended for close combat, the design of which resembles the hammer. The war hammer consists of, like the tool it resembles, a handle and a head. The handle may be of different lengths, the longest being roughly equivalent to the halberd, and the shortest about the same as a mace.

Long warhammers were pole weapons meant for use against riders, whereas short ones were used in closer quarters and from horseback. Later warhammers often had a spike on one side of the head, thus making it a more versatile weapon. Warhammers were developed as a consequence of the ever more prevalent metal armours of the medieval battlefields during the 14th and 15th centuries. The war hammer could deal blows of tremendous force to the target, especially when mounted on a pole, and by impact alone do damage without penetrating the armour. The spike end could be used for grappling the target's armour, reins, or shield, or could be turned in the direction of the blow to pierce even heavy armour. Against mounted opponents the weapon could also be directed at the legs of the horse, toppling the armored foe to the ground where they could be dealt with.

The most famous instance of a hammer as a weapon is Mjolnir, the weapon of the Norse god, Thor.

Other weapons that are types of war hammers include the pollaxes.