A military disaster is the defeat of one side in a battle or war which results in the complete failure of the losing side to achieve their objectives, often with a high and disproportionate loss of life. The causes are varied and include human error, inferior technology, logistical problems, underestimating the enemy, being outnumbered, and bad luck.

Entries on this list are those where multiple sources dealing with the subject of military disasters have deemed the event in question to be a military disaster (or an equivalent term).